shawon notes | · apparatus: toy car or tennis ball, meter rule, slotted masses, stopwatch,...

Shawon Notes | www.shawonnotes.com 2

Following the Specification of Edexcel (4PH0)

By Shawon Ibn Kamal


Qualification Content: 1) Forces and Motions:

a) Units

b) Movement and position

c) Forces, movement, shape and momentum

d) Astronomy

2) Electricity:

a) Units

b) Mains electricity

c) Energy and potential difference in circuits

d) Electric charge

3) Waves:

a) Units

b) Properties of waves

c) The electromagnetic spectrum

d) Light and sound

4) Energy, resources and energy transfer

a) Units

b) Energy transfer

c) Work and power

d) Energy resources and electricity generation

5) Solids, liquids and gases

a) Units

b) Density and pressure

c) Change of state

d) Ideal gas molecules

6) Magnetism and electromagnetism

a) Units

b) Magnetism

c) Electromagnetism

e) Electromagnetic induction

7) Radioactivity and particles

a) Units

b) Radioactivity

c) Particles

Appendix 1: Electrical Circuit Symbols

Appendix 2: Physical Units

Appendix 3: Formulae and Relationships

Appendix 4: Glossary


Section 1: Forces and motion

a) Units

1.1 use the following units: kilogram (kg), metre (m), metre/second (m/s), metre/second2

(m/s2), newton (N), second (s), newton per kilogram (N/kg), kilogram metre/second (kg

m/s).

Unit of mass=Kilogram (kg)

Unit of distance=Metre (m)

Unit of speed or velocity= Metre per second (m/s)

Unit of acceleration= metre per second2 (m/s2)

Unit of Force= Newton (N)

Unit of Time= Second (s)

Unit of gravitational acceleration= Newton per kilogram(N/kg)

Unit of Momentum= kilogram metre per second (kg m/s)

b) Movement and Position

1.2 plot and interpret distance-time graphs

Distance = The change of position of an object is called distance. The diagram shows an example:

Figure 1 shows an object changes its position from A to B. So the distance travelled by the object is AB.

Displacement = The change of position of an object in a particular direction is called displacement.

Figure 2 shows another object changes its position from C to D through curved path but the

displacement will be straight distance from C to D.


Distance-time graph

A distance-time graph represents the speed or velocity of any object. In this graph the object is moving

at 1 m per second. It is in a constant speed. In a distance-time graph, distance should go to the Y-axis

while time should go over the X-axis.

Speed= gradient=distance/time = 3m/3s= 1m/s

Few points that should be noted:

1. In a displacement – time graph or distance- time graph, the average velocity is found by the

ratio

where = change in displacement/distance and

2. A positive gradient of the displacement-time graph indicates that the car is moving in the same

direction as the displacement.

3. A negative gradient of the displacement-time graph indicates that the car is moving in the

opposite direction to the displacement.

4. A zero gradient of the displacement-time curve shows that the car is stationery.


Some explanation of motion from graph:

Zero displacement

Constant displacement

Uniform Velocity

Acceleration

Deceleration


1.3 know and use the relationship between average speed, distance moved and time:

average speed = distance moved /time taken

Speed: Speed is defined as the rate of change of distance. In other words, speed is the distance moved

per unit time. It tells us how fast or slow an object is moving.

Most objects or bodies do not move at constant speed. For example, the MRT train starts from rest at a

station, moves faster and faster until it reaches a constant speed and then slows down to a stop at the

next station. It is therefore more useful to define average speed rather than the actual speed.

Average speed: Average speed is the total distance moved divided by total time taken. If you see the

graph in 1.2 it had an average speed of 1 m/s. This is the relation between speed and distance, time.

Distance and time has no relation individually. They are both different types of values.

Instantaneous speed: The speed of an object at a particular moment is called instantaneous speed. It is

measured by taking ratio of distance travelled by shortest possible time.

Difference between speed and velocity:

Speed Velocity

i. The rate of distance travelled is speed. i. The rate of displacement travelled is velocity.

ii. Speed can be in any direction. ii. Velocity is speed in particular direction.

iii. Speed is a scalar quantity. iii. Velocity is a vector quantity.

1.4 describe experiments to investigate the motion of everyday objects such as toy cars or tennis

balls

Experiment: Measuring speed using click and stopwatch

Suppose you want to find the speed of cars driving down your road. You may have seen the police using

speed guns to check that drivers are keeping to the speed limit. Speed guns use microprocessors to

produce an instant reading of the speed of a moving vehicle, but you can conduct a very simple

experiment to measure car speed.

Measure the distance between two points along a straight section of road with a tape measure or “click”

wheel. Use a stopwatch to measure the time taken for a car to travel the measured distance.

Use the speed, distance and time equation to work out the speed of the car.


Experiment: Measuring speed using light gate method

1. Attach a cart of measured length centrally to the top of the toy car.

2. Air track ensures a frictionless way for the toy car.

3. A gentle push can move the toy car at a steady speed.

4. Arrange for the card to block a light gates beam as it passes through it.

5. Electronic timer measures how long the card takes to pass through the beam.

6. Now calculate the toy car's average velocity as it passes the light gate by:

Experiment: Measuring speed using ticker-time method

Experiment: Video (sequence) method – Measuring the velocity of a tennis ball.

A tennis ball is let to move on a track at a steady speed. During the ball moves, video the ball moving

along in front of calibrated scale (a scale where there is marking in length) attached to the slope.


Play the video back to get the snap shots taken at a time. Measure how far the ball advances between

snaps from the scale. The video camera can take 25 snaps each second. So the time between each snap

is 0.04 second.

Now calculate the balls average velocity between snaps using the following equation:

Velocity = distance moved between snaps ÷0.04

Experiment: To find out Average Speed of Toy car or trolley

Apparatus: Toy car or tennis ball, meter rule, slotted masses, stopwatch, thread.

Procedure:

1. Put toy car on bench and attach pulley to the corner of the bench as shown in figure.

2. Attach one end of the thread with toy car and other end with slotted masses while hanging them over

pulley.

3. Keep toy car & pulley one meter apart with meter rule.

4. Hold the toy with hand so that it remains there immovable.

5. Time stop watch when you let toy to move a meter distance.

6. Repeat this & record reading for different distances in the following chart.


7. Draw graph to find out average speed, which can be found by finding the gradient of the graph.

Precautions:

1. Do not hang heavier masses as this may break the thread.

2. Wear shoes as to avoid injury to foot in case of broken thread and fall of mass.

3. Put something soft under the hanging mass, like tray filled with sand.

Sources of error:

1. Reaction time

2. Ruler may not be straight

3. Parallax error

4. Friction in the bench.

Ways to improve:

1. Bench should be very polished friction.

2. Tyres of the toy should not be very rough.

3. Use light-gates instead of the stopwatch and connect light-gates to datalogger and then to computer,

to get more accurate results.

Experiment: Measuring acceleration using light gate method


• A card is mounted on the top of a trolley. The length of the card is measured.

• One light is set at the top of the track and the second one is at the end of the track.

• The trolley is given a gentle push to move through the track.

• When the trolley passes through the first light gate the electronic timer measures the t1 to cross

the length of the card.

• So the velocity at the position of first light gate is measured by velocity.

o V1= length of the first card ÷t1

• During passing the second light gate, if the time measured by electronic timer is t2 then the

velocity can be measured by:

o V2 = length of the second card ÷t2

• The time t3 is measured for the trolley to travel from first light gate to the second light gate by

using a stopwatch.

• Now acceleration is = velocity difference ÷ t3

= {(length of the first card ÷t1) - (length of the second card ÷t2)} ÷ t3

Experiment: Measuring acceleration using Video (sequence) method

Experiment: Measuring acceleration using Modern Version of Galileo’s Experiment:

Apparatus -

Light gate

Interrupter

Air pumper

Air track

Data logger or electronic timer

Diagram –


Working Procedure - We can measure the acceleration by conducting an experiment using an air-track

which can be referred as the modern-version of Galileo experiment.

From the diagram show the investigation where we can see that the air-track reduces friction because

the glider rides on a cushion of air that is pumped continuously through holes along the air track. As the

glider accelerates down the sloping track the white card mounted on it breaks a light beam, and the

time the glider takes to pass is measured electronically. If the length of the card is measured, and this is

entered into the spreadsheet, the velocity of the glider can be calculated by the spreadsheet

programme using v = d/t.

Observation - Here from the above procedure it is observed that the distance travelled in equal intervals

is increased and that the rate of increase of speed is steady or uniform i.e. it is uniform acceleration.

Table and Graph

Conclusion

The gradient of a velocity-time graph gives the acceleration


Experiment: Measuring acceleration using double light gate.

1. A card is mounted on the top of a trolley.

2. The length of the card is measured.

3. One light gate is at the top of the track and another light gate is at the end of the track.

4. The trolley is given a gentle push to move through the track.

5. When the trolley passes through the first light gate, the electronic timer measure the time (t1) to cross

the length of the cord.

6. So the velocity at the position of first light gate is measured by:

7. The time, t3 is measured for the trolley to travel from first light gate to 2nd light gate by using a

stopwatch.

8. Now,

=

Experiment: Measuring acceleration using ticker tape.

Apparatus: Ticker timer and tape, a.c. power supply, trolley, runway


Procedure:

1. Set up the apparatus as in the diagram.

2. Connect the ticker timer to a suitable low-voltage power supply.

3. Allow the trolley to roll down the runway.

4. The trolley is accelerating as the distance between the spots is increasing.

5. The time interval between two adjacent dots is 0.02 s, assuming the ticker timer mars fifty dots per

second.

6. Mark out five adjacent spaces near the beginning of the tape. Measure the length s1.

7. The time t1 is 5 × 0.02 = 0.1 s.

8. We can assume that the trolley was travelling at constant velocity for a small time interval.

Thus initial velocity u = distance/time = s1/t1

9. Similarly mark out five adjacent spaces near the end of the tape and find the final velocity v.

10. Measure the distance s in metres from the centre point of u to the centre point of v.

11. The acceleration is found using the formula: v2 = u2 + 2as or a = v2 – u2 / 2t

12. By changing the tilt of the runway different values of acceleration are obtained. Repeat a number of

times.

13. Tabulate results as shown.

1.5 know and use the relationship between acceleration, velocity and time:

Acceleration is the rate at which objects change their velocity. The rate of decease of velocity is called

acceleration. It is just a negative acceleration. It is defined as follows:

Acceleration=change in velocity/time taken

or

(final velocity-initial velocity) /time taken

This is written as an equation:


where a=acceleration, v=final velocity, u=initial velocity and t=time

1.6 plot and interpret velocity-time graphs

Velocity-time graphs represent the acceleration of any object. Velocity(m/s) is in the Y-axis while Time is

the X-axis.

Some common velocity-time graphs:


1.7 determine acceleration from the gradient of a velocity-time graph

Acceleration = gradient

=

=

= 4 m/s2

1.8 determine the distance travelled from the area between a velocity-time graph and the time axis.

Distance can be determined by finding the area of the triangle of a velocity-time graph as shown below:

#

Distance travelled = area under the graph

= ½ (a+b)h


= ½ (100 + 40) x 150

= ½ x 140 x 150

= 10500m

#

i) Acceleration in first 60s =

=

=

m/s2

ii) Distance in 100s = ½ x b x h + l x b

= ½ x 60 x 40 + 40 x 60

= 1200 + 2400

= 3600 m

iii) Average Speed =

= 2800/100

= 28 m/s


#

Maximum speed = 60 m/s

Acceleration =

Part – 1 =

=

= 3 m/s

Part – 2 =

=

= 2 m/s

Part – 3 =

=

= 4 m/s2

c) Forces, movement, shape and momentum

1.9 describe the effects of forces between bodies such as changes in speed, shape or

direction

Force is that which can change the state of rest or uniform motion of an object. Force is simply pushes

and pulls of one thing on another.

If a body is thrown up in the air, what is the effect of gravity on the body? At first gravity reduces the

speed of upward movement of the body and at a certain height it stops. So Force effects the speed.

Take a sponge and squeeze it will change its shape.


Throw a ball at a person in one direction. That person will hit the ball again i.e. apply force to the ball

and it will change its direction.

To sum up the examples, the effects that occur when a force is applied to an object are:

1. The object may start to move or stop moving.

2. The object may speed up or slow down.

3. The object may change its shape

4. The object may change its direction of movement.

1.10 identify different types of force such as gravitational or electrostatic

Different sorts of Force:

1) Gravitational force or weight: The pull of earth due to gravity.

2) Normal Reaction: Simple reaction that stops something when to apply force to it. E.g.: A book is

kept on the table which has a normal reaction on it. Otherwise the book would fall down.

3) Air Resistance: The resistivity or drag in the air while an object moves is called Air Resistance.

E.g.: When a parachutist open the parachute the movement slows down for the opposite force

acting in it.

4) Upthrust: Upthrust force acts only on liquid or air. It pushes an object upwards inspite of gravity.

E.g.: A helium balloon moves upwards due to up thrust force.

5) Magnetic: Magnetic force is the attraction force between the poles of magnets. N=S

6) Electrostatic: Electrostatic force is the attraction force between charges. + = -

7) Tension: The pull at both ends of a stretched spring ,string, or rope.

8) Frictional force: the force produced when two objects slide one over another is called frictional

force.

1.11 distinguish between vector and scalar quantities

Scalar quantities are physical quantities that have magnitude only. For example, mass and distance are

two scalar quantities.

Vector quantities however are physical quantities that possess both magnitude as well as direction.

Examples of vector quantities are force, velocity and acceleration.

Scalar Vector Mass Displacement

time Velocity

Distance Acceleration

Speed force

Volume

Density

Work

Energy

power


Difference:

Scalar Vector

Needs only size to express them Needs both size and direction to express them.

Changes by changing size. Changes by changing size or direction or even both.

Product of two scalar is a scalar i.e scalar X scalar = scalar.

Products of two vectors can be either be scalar or vector i.e. vector X vector = scalar/vector.

1.12 understand that force is a vector quantity

Force is a vector quantity due to the following reasons -

• It has magnitude i.e has the value of its size.

• It has direction.

• When applied force, an object moves with particular motion in a fixed direction.

E.g: Gravitational force has one direction which is downwards. Upthrust has the direction of upwards.

1.13 find the resultant force of forces that act along a line

Forces which act along a straight line can be added if the forces are in the same direction or subtracted

if the forces are in the opposite direction. The force that you get after adding or subtracting is called the

resultant force. The resultant force is a single force that has the same effect as all the other forces

combined.

Figure 1 Figure 2

Figure 1 shows that two forces: 150N and 50N are acting on an object A in the same direction and the

object is moving.

Figure 2 shows that a single from 200N is acting on the same object and the object moves at the same

motion. So 200N is the resultant force of 150N and 50N.


Examples are -

i.

Resultant force = (500 - 500)N

= 0 N (rest object)

ii.

Resultant force = (500 - 200)N

= 300 N (towards right)

iii.

Resultant force = 600 N (towards right)

iv.

Resultant force = 1000 – 1000

= 0 N (rest object)


1.14 understand that friction is a force that opposes motion

Friction is the force that causes moving objects to slow down and finally stop. The kinetic energy of the

moving object is converted to heat as work is done by the friction force. Friction occurs when solid

objects rub against other solid object and also when objects move through fluids (liquids and gases).

Types of frictions:

• Kinetic friction: The friction that occurs when the object is in motion is called kinetic friction. E.g:

Friction deduced in a moving car.

• Static friction: The friction produced when force is applied but the object doesn’t move is called

static friction. E.g: a block is pulled but it doesn’t move because the force is not enough to move

it. The friction produced in the block in this situation is the static friction.

• Rolling friction: When an object rolls around another object, a friction is produced. This is called

rolling friction. E.g.: The car wheel moves around the axel and rolling friction is produced.

• Fluid friction: The friction produced when two liquid layer side by side moves at different speed

is called fluid friction.

• Solid-fluid friction: When a solid moves through a fluid, a friction is produced to the motion. This

is called solid-fluid friction.

Causes of friction:

• Ridges and bumps between the surfaces.

• The attraction force between the molecules of containing surfaces.

Ways to reduce friction:

• By making the surface smooth,

• By using lubricating oil such as mobile, grease etc.

Advantages of friction:

• We can walk and run due to friction.

• We can fix a nail in the wall due to friction.

• We can hold a pen due to friction.

Disadvantages of friction:

• Friction causes wear and tear in the surface.

• It reduces the efficiency of the machines.

• There is wastage of energy due to friction.


Experiment: To investigate friction

As shown on the diagram above, a block is set on the surface of the track. A nylon line is connected to it

which passes over a pulley to a weight. There is friction between the surface of the block and the

surface of the track. When the pull of weight equals to the friction then the block starts moving. So the

amount of the weight that starts the block to move is equal to the friction.

We can increase the friction by putting some masses over the and we will see that the more is the mass

the more is the friction. We can make the track surface rougher such as by using sand paper we will see

the friction increases.

1.15 know and use the relationship between unbalanced force, mass and acceleration:

Balanced force - When two or more forces acting on an object cancels each other and there is no

resultant force, then the forces are called balanced force.

200N and 300N are acting towards left on the object A. 500N force is acting on it towards right. The

forces cancel each other. So there is no resultant force. So these forces are called balanced forces.

Unbalanced force - When two or more forces acting on an object do not cancel each other fully and

there is a resultant force, then the forces are called unbalanced force.


400N and 200N are acting on the object A towards right direction. 300N is acting towards left direction.

The forces do not cancel each other fully. There is resultant force of 300N towards right. So their forces

are unbalanced.

Force= mass x acceleration

In equation, F=ma (where, m=mass and a=acceleration)

F α a

Force is directly proportional to acceleration. If force increases acceleration increases.

Experiment: To investigate F α a

Working principle - The rate of change of momentum is directly proportional to the applied force and

takes place in the direction of force.

Apparatus required -

• Trolley

• Nylon line

• Pulley

• Ramp

• Bench top

• Mass hanger

Diagram -


Working procedure -The force acting on the trolley is produced by the masses on the end of the nylon

line. As the mass is increased, the trolley accelerates as well, so the force is increased by the transferring

one of the masses from the trolley to the mass hanger.

In the diagram-b, this increases the pulley force on the trolley, while keeping the total mass of the

system the same. The acceleration of the trolley can be measured by taking a series of pictures at equal

intervals of time using a digital video camera.

Observation -Here, using the digital video camera, as sequences of pictures are taken, the distance

travelled from the start for each image is measured, since the time between each image is known, a

graph of displacement against time can be drawn. The gradient of the displacement-time graph gives

the velocity at a particular instant, so using the value data for a velocity-time graph can be obtained. The

gradient of the velocity-time graph produced is the acceleration of the trolley.

Graph -

Conclusion -The force and acceleration is same and this produces a straight-line graph which determines

that force is directly proportional to force. So doubling the force acting on an object doubles its

acceleration.

Experiment: To investigate a α 1/m

The same experiment as above, only the force is kept constant and the mass of the trolley is varied.


The graph shows the acceleration of the trolley plotted against 1/m. This is also a straight line passing

through the origin, showing that acceleration is inversely proportional to mass.

a α 1/m

This means that for a given unbalanced force acting on a body, doubling the mass of the body will halve

the acceleration.

Combining Experiment 1 and 2, we get:

F = m xa

One newton is the force needed to make a mass of one kilogram accelerate at one metre per second

squared.

1.16 know and use the relationship between weight, mass and g:

Weight is the pull of earth. To calculate it, use the formula:

Weight = mass x gravitational acceleration

W =m g

Gravitational field strength: The pull of planet on an object of 1 kilogram is called gravitational field

strength. It is also denoted by g, where in earth g= 10 m/s2 if there is no opposite force.


Experiment: To verify acceleration due to gravity using video camera

We could measure the distance between two images of the tennis ball – say, the second and the third.

This is the distance that the ball travelled during the second interval of one tenth of a second. The

average velocity during this time is found by diving the distance travelled, 14.7 cm, by the time taken,

0.1s. This gives an average velocity of 147 cm/s or 1.47 m/s over the interval. If we repeat the

calculation for the next tenth of a second, between 3 and 4m we find the average velocity has increased

to 2.45 m/s. We can then use the equation for acceleration.

The result of this experiment gives us a value for acceleration caused by the force of gravity.

Experiment: To measure acceleration due to gravity using electromagnet

Apparatus: Millisecond timer, metal ball, trapdoor and electromagnet.


Procedure:

1. Set up the apparatus as shown. The millisecond timer starts when the ball is released and stops when

the ball hits the trapdoor.

2. Measure the distance, s using a meter stick.

3. Flick the switch to release the ball and record the time, t from the millisecond timer.

4. Repeat for different values of s.

5. Calculate the values of g using the equation s = (g/2) t2. Obtain an average value for g.

6. Draw a graph of s against t2 and use the slope to find the value for g.

Precautions/ Source of error:

1. For each height s repeat three times and take the smallest time as the correct value for t.

2. Place a piece of paper between the ball bearing and the electromagnet to ensure a quick release.

3. Remember to convert from milliseconds to seconds.

1.17 describe the forces acting on falling objects and explain why falling objects reach a

terminal velocity

Terminal velocity is the steady velocity of a falling object whose drag is balanced by the weight.


How does a falling object reach terminal velocity?

In a free falling object two types of force acts: Drag and Weight. The size of the drag force acting on an

object depends on its shape and its speed. If the drag force of an object increases to a point which is

equal to Weight, then the acceleration stops. It falls in a constant velocity known as terminal velocity.

Reaching terminal velocity on a parachute:

When a skydiver jumps from a plane at high altitude he will accelerate for a time and eventually reach

terminal velocity. When she will open her parachute, this will cause a sudden increase in the drag force.

At that time drag force will be higher than the weight and he will decelerate for some time. Later those

forces will become equal and reach a new terminal velocity.


1.18 describe experiments to investigate the forces acting on falling objects, such as

sycamore seeds or parachutes

Sycamore seeds:

We can measure the weight of the sycamore seeds using an electric balance. Now the sycamore seed is

released from a high point. We will use a digital video camera to take the snaps of the moving seed. The

video camera can take 25 snaps in one second. We can measure the acceleration of the ball at any point

using the snaps of the moving seed. Now multiplying the mass of the seed by acceleration at any point

we can find the unbalanced force acting on it. If we subtract the unbalanced weight from its weight, we

will get the air resistance acting on the seed.

Parachutes:

When a parachute is released only the weight acts on it. We can use a force meter to determine the

weight. When the parachute falls downward, air resistance acts on it in the upward direction. So the

downward unbalanced force decreases. The force meter attached to the parachute gives a lower

reading. As the parachute goes down the speed increases. The drag force also increases. The reading on

the force meter decreases as well. A moment comes when the drag force becomes equal to the weight.

In this situation the reading in the force meter becomes zero. If we want to find the air resistance at any

momentum we will have to subtract the weight from the unbalanced force. This is how we can

investigate the forces acting on a falling object.

1.19 describe the factors affecting vehicle stopping distance including speed, mass, road

condition and reaction time

Stopping distance: The stopping distance is the sum of Thinking distance and Braking distance.

Thinking distance: The distance travelled after seeing an obstacle and till reaction.

Braking distance – The distance travelled after the brakes are applied.

The thinking distance depends on the following factors -

i. Whether the driver is tired or has taken alcohol or drugs.

ii. On the visibility power of the driver.

iii. On the speed of the car.

The braking distance depends on the following factors -

i. Speed of the car: The more the speed is, the more the braking distance will be; S α V2.

ii. Mass of the car: As acceleration is equal to F/m, for constant braking force, the more

is the mass, the less is the deceleration, the more is the braking distance.

iii. Road condition: If the road is rough, the braking distance will be less.

iv. Tyre condition: If the tyre is new (rough), there will be less braking distance.

v. Braking system: For loose braking system, the braking distance will be more.


1.20 know and use the relationship between momentum, mass and velocity:

Momentum is a quantity possessed by masses in motion (product of mass and velocity). Momentum is

measure of how difficult it is to stop something that is moving. We calculate the momentum of a moving

object using the formula:

Momentum, p(kg m/s) = mass, m(in kg) x velocity, v (in m/s)

P= m x v

1.21 use the idea of momentum to explain safety features

1 Crumple Zone

Cars are now designed with various safety features that increase the time over which the car’s

momentum changes in an accident. Crumple zones are one of the safety features now used in modern

cars to protect the passengers in an accident. The car has a rigid passenger cell with crumple zones in

front and behind. During a collision, it increases the time during which the car is decelerating. This also

reduce the force impacting on the passenger increasing their chances of survival.

2 Air Bags


Many cars are now fitted with air bags to reduce the forces acting on passengers. The purpose of an

airbag is to help the passenger in the car reduce their speed in collision without getting injured.

Objects in a car have mass, speed and direction. If the object, such as a person, is not secured in the car

they will continue moving in the same direction (forward) with the same speed (the speed the car was

going) when the car abruptly stops until a force acts on them.

Every object has momentum. Momentum is the product of a passenger's mass and velocity (speed with

a direction). In order to stop the passenger's momentum they have to be acted on by a force. In some

situations the passenger hits into the dashboard or windshield which acts as a force stopping them but

injuring them at the same time.

An airbag provides a force over time. This is known as impulse. The more time the force has to act on

the passenger to slow them down, the less damage caused to the passenger.

1.22 use the conservation of momentum to calculate the mass, velocity or momentum of

objects

If a moving object hits another slow or stationary object, it will result a equal force to both of the objects

(according to Newton’s Third Law). That forces act in opposite directions and obviously for the same

amount of time. This means the F x t for each is the same size. The moving object losed its momentum

while the stationary object gained its momentum. So it is balanced. The total moment of the two objects

is unchanged before and after the collision- momentum is conserved.

Momentum before the collision = momentum after the collision

m1u1 + m2u2 = m1v1 + m2v2.

Elastic and inelastic collisions

In a collision, if the kinetic energy remains conserved, the collision is called elastic collision.

Example- Collision between two gas molecules.

In a collision if the kinetic energy does not remain conserved, the collision is called inelastic collision.

Example - Collision between a truck and a micro-bus.


Application of momentum principle: Explosion

Two gliders are tied by a thread while the two ends contain two like poles of a magnet. The gliders are

on the air track. Using a match stick we can burn the thread. When the thread is cut, the two gliders

move away in opposite direction. If the masses of the two gliders are same, the speed of the gliders will

also be equal. It means that the momentum of the two gliders is equal and opposite. That is the total

momentum difference is zero which was the same before the collision. It verifies the law of conservation

of momentum.

Before collision After collision

Both rest Both can stop

Both moving Both moving (same/ opposite)

One moving Both can be one object

Law of conservation of momentum is only verified if two forces act on it-- action & reaction.

Application of momentum principle: Rockets

Rocket motors use the principle of conservation of momentum to propel spacecraft through space. They

produce a continuous, controlled explosion that forces large amount of fast-moving gases (produced by

fuel burning) out of the back of the rocket. The spacecraft gains an equal amount of momentum in the

opposite direction to that of the moving exhaust gases and moves upward with a very high speed.

1.23 use the relationship between force, change in momentum and time taken:

Initial momentum of object = mu

Final momentum = mv

Therefore increase in momentum = mv-mu

Rate of increase of momentum = (mv-mu)/t = m(v-u)/t = ma = Force

Force = Rate of increase of momentum

Force = Change in momentum / time


1.24 demonstrate an understanding of Newton’s third law

Newton’s thirds law: “For every action there is an equal and opposite reaction.”

Newton’s third law states four characteristics of forces:

Forces always occur in pairs (action and reaction force.)

The action and reaction are equal in magnitude.

Action and reaction act opposite to one another.

Action and reaction act on different bodies.

Action and reaction do not cancel each other

1.25 know and use the relationship between the moment of a force and its distance from

the pivot:

moment = force × perpendicular distance from the pivot

moment =F x d

The turning effect of a force about a hinge or pivot is called its moment. In other words, it is the product

of force and the perpendicular distance from the pivot to the line of action of the force. It is measured in

Newton meter (Nm).


There are two types of moment: (i) Clockwise moment & (ii) Anti-clockwise moment

When a force causes an object to turn in a clockwise direction, it is called a Clockwise Moment.

When a force causes an object to turn in an anti-clockwise direction, it is called a Anti-clockwise

moment.

1.26 recall that the weight of a body acts through its centre of gravity


Mass is the amount of matter an object has. Every part of an object forms part of its overall mass. But

when we try to balance an object on a point, there will only be one place where it will balance. You can

therefore think of the mass of an object being concentrated at this point, known as the centre of mass

or gravity.

If we support the centre of gravity of the object, the object won’t fall no matter how wide it is. Because

the moment of the all sides are balanced and there will be no clockwise or anti-clockwise movement.

Stability of centre of gravity

A stable object is one that is difficult to push over; when pushed and then released it will tend to return

to its original position. Stability can be increased by:

i. By increasing the base area.

ii. By decreasing the height of COG.


Experiment: To determine the position of the centre of gravity of an uniform object using balancing

method

Balance the object keeping over a scale and draw the line of contact. Balance the object on another axis

keeping it over the same scale and draw the line of contact again. The two lines intersect at a point. This

point gives the COG.

Experiment: To determine the position of the centre of gravity of a plane lamina with irregular shape of

non-uniform thickness or density

Apparatus: Retord stand, plumbline, cork and pin

Procedure:

1. Make three small holes near the edge of the lamina. The holes should be as far apart as possible

from one another.

2. Suspend the lamina through one of the holes using a pin.

3. Hang a plumbline on the pin in front of the lamina.

4. When the plumbline is steady, draw a line on the lamina over the plumbline.


5. Repeat the above for other two holes.

6. The point of intersection of the three lines is the position of the centre of gravity.

Precautions:

1. The holes must be small so that not too much of the lamina is removed.

2. The lamina should be free to swing above its point of suspension.

1.27 know and use the principle of moments for a simple system of parallel forces acting in

one plane

Solving Problems related to Principle of Moments

Example - 1

Step 1:

Identify what are forces that will give rise to clockwise / anti-clockwise moment


Step 2:

Find the clockwise / anticlockwise moment

Step 3:

Equate the clockwise and anticlockwise moments


Example – 2

F2 d2 + F1 d1 = F3 d3 + F4 d4

10 x 20 + 20 x 10 = 5 x 20 + 15 x d4

400 – 100 = 15 x d4

d4 = 300/15

d4 = 20m

Example – 3


At position A, the object is of 400N at a distance 1.5m from the pivot. What should be the distance of

object B from the pivot is of 500N and the see-saw is at equilibrium position.

At equilibrium, sum of clockwise moment = sum of anti-clockwise moment

F1 d1 = F2 d2

400 x1.5 = 500 x d2

d2 = 600/500

d2 = 1.2 m

Example – 4

In a crane, the force arm d1 = 2m and weight of 5000N is put at the force arm. What maximum load the

crane can raise in the load arm d2 is 10m?

Sum of CWM = Sum of ACWM

W x d1 = F x d2

F =

F =

F = 1000N


Experiment: To verify the principle of moment

A uniform beam AD is put at point P on a support.

The beam is balanced.

Now, we will put four different beam at different distances in a way so that the beam restores the

balance again.

Now, calculate the moment for the weights

Moment for W1 = W1d1




Now, sum of clockwise moments = W3d3 + W4d4

Sum of anti-clockwise moments = W1d1 + W2d2

Now, if we put the values of constants, we will see that W1d1 + W2d2 = W3d3 + W4d4

i.e. Sum of anti-clockwise moment = sum of clockwise moment

So the principle of moment is verified.


1.28 understand that the upward forces on a light beam, supported at its ends, vary with the

position of a heavy object placed on the beam

a) An object weighing 400 N is placed in the middle of the beam. The beam is not moving, so the upward

and downward forces must be balanced.

b) As the object is placed in the middle of the beam, the upward forces on the ends of the beam are

same as each other. If it is moved right to one end of the beam, then the upward force will all be at that

end of the beam. As it is moved along the beam, the upward forces at the ends of the beam change.

In c) he is ¼ away from the plant. The upward force on the support nearest to him is ¾ of his weight and

the upward force on the end of furthest beam is only ¼ of his weight.


1.29 describe experiments to investigate how extension varies with applied force for

helical springs, metal wires and rubber bands

Experiment: Investigating extension with applied force in spring

Apparatus:

Spring/Wire/Rubber-band

Scale

Some masses

Clamp and stand

Mass hanger

Working procedure:

i) Take the length of the normal condition.

ii) Add a mass in the mass hanger and determine the extension by using the porter and the scale.

iii) Add another mass gradually and determine the extension in all cases.

iv) Plot a graph of extension and relevant loads.


Observation with helical spring:

Since the graph of load & extension is a straight line, which proves the extension and load are directly

proportional.

Observation with rubber band:

Since the graph didn’t produce a straight line, extension is not directly proportional to load force. But

extension still increases as the force is applied.


Observation with metal wire:

1.30 understand that the initial linear region of a force-extension graph is associated with

Hooke’s law

Hooke’s law, “Within the elastic limit, extension is directly proportional to the load i.e. e α f”

Hooke measured the increase in length (extension) produced by different load forces on springs. The

graph he obtained by plotting force against extension looked like that below. This straight line passing

through the origin shows that the extension of the spring is proportional to the force. The relationship is

known as Hooke’s law.

Hooke’s Law only applies if you do not stretch a spring to far. At a point the elastic limit it starts to

stretch more for each successive increase in the load force. Once you have stretch a spring beyond this

limit it has changed shape permanently and will not return to its original shape.


1.31 describe elastic behaviour as the ability of a material to recover its original shape after

the forces causing deformation have been removed.

Objects showing elastic behaviour has the ability to return to its original shape after the forces causing

its shape are removed. This property is called elasticity. Examples of objects showing elastic behaviour

are coiled springs.

Uses of spring:

1. use to absorb bumps in the road or suspension spring in the car or cycle.

2. In beds and furnitures they used to make sleeping and sitting more comfortable.

3. used in door locks to hold bolts and catches closed and to make doors close

automatically.

4. used in measuring devices like spring balance or bathroom scales.

The materials which do not exhibit elasticity i.e. they do not return to its original position after

stretching force is removed are called plastic materials. Examples are putty, plasticine.

d) Astronomy 1.32 understand gravitational field strength, g, and recall that it is different on other

planets and the moon from that on the Earth

The strength of gravity on a planet or moon is called its gravitational field strength. But this force

depends upon

1) The masses of the two objects

2) The distance between the masses


The greater the mass the greater the gravitational force. As the mass in everyday objects are less,

gravitational force is almost negligible. It is noticeable in planets, stars, sun etc.

The greater the distance the lower the gravitational force. If you move 50000 km away from Earth, you

won’t fall down as the force is between you and the earth is very weak.

F α 1/d2

Gravitional Field Strength of Planets and Moon

1.33 explain that gravitational force:

causes moons to orbit planets

causes the planets to orbit the sun

causes artificial satellites to orbit the Earth

causes comets to orbit the sun


How a planet does moves around the orbit?

Planets travel in orbits around the Sun. They must have a force applied to them. This force is the

gravitational attraction between two masses. Our Sun contains over 99% of the mass of the solar

system. It is the gravitational attraction between these mass and each of the planets that holds the solar

system together and causes the planets to follow their curved path.

What is the shape of orbit of the planets and comets?

The shape of orbit of the planets are elliptical with the Sun close to the centre.

The orbits of the comets are very elongated and elliptical. At times they are very close to the Sun, while

at other times they are found at the outer reaches of the solar system.

How are planets held in the orbit?

Planets are held in the orbit by the gravitational pull of the Sun. The gravitational pull on the Mercury is

quite large compared with the exerted on Neptune. This is the reason Mercury follows a much more

tightly curved path that Neptune.

*[If an object moves in a round path, a force is created it is called centripetal force which pushes an object the

other/opposite side]

1.34 describe the differences in the orbits of comets, moons and planets

Planets: Planets orbit the Sun. The closest planet follows a much more tightly curved path than the

furthest one. They all move in ellipses.

Moons: Moons orbit a planet. The Earth has just one moon. The Moon, like the Earth spins on its axis,

but much more slowly than the Earth turns. It completes one full rotation every 29.5 days. Because the


time it takes to complete one orbit around the Earth is the same as the time for one rotation. The Moon

always keeps the same part of its surface facing the Earth.

Comets: Comets orbit the Sun. They are approximately 1 to 30 kilometer in diameter and are made up of

dust and ice. Their orbits are very elongated. At times they are very close to the Sun, while at other

times they are found at the outer reaches of the Solar System. As a comet gets close to the Sun, the

gravitational forces acting upon it increase and it speeds up. In some of the comets, the frozen gases

evaporate, forming a long tail that shines in the sunlight. At the opposite end of its orbit, a long way

from the Sun, the gravitation forces are smaller, so the comet travels at its slowest speed.

Asteroids: Asteroids are minor planets or rocks that orbit the Sun. There is a belt of asteroid between

the orbits of Mars and Jupiter. They vary greatly in size from just a few meters to several hundred of

kilometers across. The first asteroid to be discovered was cares and has a diameter of 933 km. It is

believed that asteroids were formed at the same time as the rest of the solar system and possibly are

the rocky remains of planet that broke apart or failed to form.

Satellites: Satellites are the objects that orbit a planet. They are held in orbit by gravitational forces.

There are two types of satellites. These are natural satellites and artificial satellites. Moon is an example

of natural satellites. Some objects that orbit the planets are manufactured objects. They are known as

artificial satellites.

1.35 use the relationship between orbital speed, orbital radius and time period:

The speeds of satellites vary greatly depending on the tasks they are performing. The speed of satellite

can be calculated using the equation:

Example: Calculate the speed of a satellite that is orbiting 200km about the Earth's surface and

completes one orbit in 1 hour 24 minutes. The radius of the Earth is 6400 km.

Orbital period = 1 hr 24 min

= (60 + 24) min

= 84 min

= 84 X60s

= 5040 seconds

Orbital speed =

= [2 π X (6400+200) X 1000]÷5040 = [2 π X 6600000] ÷ 5040 = 8200 m/s


1.36 understand that:

the universe is a large collection of billions of galaxies

a galaxy is a large collection of billions of stars

our solar system is in the Milky Way galaxy.

The Universe is mainly empty space within which are scattered large numbers of galaxies- astronomers

believe that there are billions of galaxies in the Universe. The distances between galaxies are millions of

times greater than the distances between stars within a galaxy.

Gravitational forces between stars cause them to cluster together in enormous groups called galaxies.

Galaxies consist of billions of stars. Our galaxy is called spiral galaxy or the Milky Way.

Solar system consists of planets orbiting the Sun. Our solar system is a part of Milky Way galaxy.


Section 2: Electricity

a) Units 2.1 use the following units: ampere (A), coulomb (C), joule (J), ohm (

watt (W).

Unit of current: ampere (A)

Unit of charge: coulomb (C)

Unit of energy: Joule (J)

Unit of resistance: ohm (Ω)

Unit of time: second (s)

Unit of voltage or potential difference: volt (V)

Unit of Power: watt (W)

b) Mains electricity 2.2 understand and identify the hazards of electricity including frayed cables, long cables,

damaged plugs, water around sockets, and pushing metal objects into sockets

Mains electricity: The source of electricity in our houses is called mains electricity.

Electricity meter: The meter that measures the electrical energy we consume in our house is called

electricity meter.

Fuse box(or Consumer unit): The box that contains all fuse and circuit breakers in a circuit is called fuse

box.

Ring main circuit: Wires that leave the fuse box are hidden in the walls or floors around each room.

These wires are connected to form ring main circuits. Individual equipments are connected to these

circuits using plugs. It consists of three wires: live wire, neutral wire and earth wire.

Live wire: The wire that contains the electricity all the time is called live wire.

Neutral wire: The wire that usually doesn’t contain the electricity but when it is connected with the live

wire then it also become live. The neutral wire completes the circuit.

Earth wire: The earth wire usually has no current flowing through it. It is there to protect user if an

appliance develops a fault.


Electricity is very useful, but it can be dangerous if it is not used safely. The following hazards that

increase the chances of severe and possibly fatal electric shocks are:

frayed cables, any damaged insulation can expose ‘live’ wires.

Long cables, as they are more likely to get damaged or trip people up.

Damage to plugs or any insulating casing on any mains operated devices.

Water around electric sockets or mains operated devices.

Pushing metal objects into the mains sockets – usually only a problem with very young children,

solved by using socket covers.

2.3 understand the uses of insulation, double insulation, earthing, fuses and circuit

breakers in a range of domestic appliances

Insulation: Some appliances are cased with insulators like plastic rather than metal to prevent user from

receiving shock. This casing is called insulation.

Double Insulation: Some appliances are double insulated; as well as all their wiring being insulated the

outer casing of the appliances is also made of an insulating material. This means there is no chance of an

electric shock from the casing – double insulation is often used with electric kettles and power tools like

electric drills.

Earthing: Many appliances have a metal casing. This should be connected to earth wire so that if the live

wire becomes frayed or breaks and comes into contact with the casing, the current will pass through the

earth wire rather than the user. The current in the earth wire is always large enough to blow the fuse

and turning off the circuit. So the user is safe from electric shock.

Fuses: Fuse is a safety device usually in the form of a cylinder or cartridge which contains a thing piece of

wire made from a metal that has low melting point. If too large a current flows in the circuit the fuse

wire becomes very hot and blows, shutting the circuit off. This prevents you getting a shock and reduces

the possibility of an electrical fire. One the fault in the current is corrected, it should be replaced again.


Circuit Breakers or Trip switches: Circuit Breaker is similar to fuses. If too large a current flows in a

current a switch opens making the circuit incomplete. Once the fault in the circuit is corrected, the

switch is reset, usually by pressing a reset button.

inside

outside

How does a circuit breaker work?

When high current flows, the electromagnet in it gains its magnetism and attract the iron catch towards

it. This separated the contact and the circuit discloses.

Switches: Switches in main circuit should always be included in the live wire so that when the switch is

open, no electrical energy can reach an appliance. If the switch is included in the neutral wire, electrical

energy can still enter an appliance, and could possibly cause an electric shock.


2.4 understand that a current in a resistor results in the electrical transfer of energy and an

increase in temperature, and how this can be used in a variety of domestic contexts

Normal wiring in the house are said to have low resistance and the current pass through them easily.

Heating elements like nichrome wire have high resistance. When current flows through them current

cannot pass, and the energy is transferred to heat energy and the element heats up. It is also used in the

lights – normal light bulbs have a very thin filament which gets so hot when current passes through it

that it glows white. We use the heating effect of current in electric kettle, iron, filament lamps, fan

heaters, hair dryers etc.

2.5 know and use the relationship:

power = current × voltage

P = I × V

and apply the relationship to the selection of appropriate fuses

Power is amount that represents how much voltage or energy is converted every second. It is calculated

using this equation:

Power, P (in watts) = current, I (in amps) x voltage, V (in volts)

P= I x V

Fuses in plugs are made in standard ratings. The most common are 3A, 5A and 13A. The fuse should be

rated at a slightly higher current than the device needs:

if the device works at 3A, use a 5A fuse

if the device works at 10A, use a 13A fuse

2.6 use the relationship between energy transferred, current, voltage and time:

energy transferred = current × voltage × time

E = I × V × t


The power of an appliance (P) tells you how much energy it converts each second. This means that the

total energy (E) converted by an appliances is equal to its power multiplied by the length of time the

appliance is being used.

Total energy, E(in joules) = power, P (in watts) x time, t (in seconds)

E= P x t

Since, P = I x V

E= I x V x t

2.7 understand the difference between mains electricity being alternating current (a.c.) and

direct current (d.c.) being supplied by a cell or battery.

Alternating current:

If the current constantly changes direction, it is called alternating current, or a.c.. Mains electricity is an

a.c. supply, with the UK mains supply being about 230V. It has a frequency of 50Hz (50 hertz), which

means it changes direction, and back again, 50 times a second. The diagram shows an oscilloscope

screen displaying the signal from an a.c. supply. Alternating current is useful in electricity generator and

transformers.


Direct current:

If the current flows in only one direction it is called direct current, or d.c. Batteries and cells supply d.c.

electricity, with a typical battery supplying maybe 1.5V. The diagram shows an oscilloscope screen

displaying the signal from a d.c. supply.

Alternating current can be converted to direct current by using a rectifier. This direct current is made

uniform by filter circuit.


c) Energy and potential difference in circuits 2.8 explain why a series or parallel circuit is more appropriate for particular applications,

including domestic lighting

Series Circuit:

one switch can turn off the components on and off together

if one bulb ( or other component) breaks, it causes a gap in the circuit and all of the other bulbs

will go off

the voltage supplied by the cell or mains supply is “shared” between all the components, so the

more bulbs you add to a series circuit the dimmer they all become. The larger the resistance of

the component, the bigger its “share of voltage”

Parallel Circuit:

switches can be placed in different parts of the circuit to switch each bulb on and off individually

or all together

if one bulb (or other components) breaks, only the bulbs on the same branch of the circuit will

be affected

each branch of the circuit receives the same voltage, so if more bulbs are added to a circuit in

the parallel they all stay bright.

Decorative lights are usually wired in series. Each bulb only needs a low voltage, so even when the

voltage from the mains supply is shared between them, each bulb still gets enough energy to produce

light. If one of the bulbs is not in its holder properly, the circuit is not complete and none of the bulbs

will be on. In the past, if the filament in one of the bulbs broke, all of the other bulbs would go out.

Today, many bulbs used in decorative lights are provided with a ‘shunt’ which allows current to continue

to flow through the bulb even after the filament has broken.

The lights in our house are wired in parallel. Each bulb can be switched on and off separately and the

brightness of the bulbs does not change. If one bulb breaks or is removed, you can still use the other

lights.

2.9 understand that the current in a series circuit depends on the applied voltage and the

number and nature of other components

Series circuit: In a series circuit the current is the same in all parts. Current is not used up as it passes

around a circuit.

The size of the current is a series circuit depends on the voltage supplied to it, and the number and

nature of the other components in the circuit. In a circuit if more cell is attached, the current will

increase as more energy is being given to the electrons. If more resistance is attached to the circuit the

current will get less. But current is same at all points in a series circuit.


Parallel circuit: In parallel circuit, current varies with the resistance and voltage. Voltage are same at all

branches.

This circuit shows a 10 Ω and 20 Ω resistor connected in parallel to a 6V cell of negligible internal

resistance. The p.d. across 10 Ω and 20 Ω resistors is 6V.

I1 = 0.6A

I2 = 0.3 A

As the resistance in I2 is higher, the current is small.

I3 = I1 + I2 The current in a parallel circuit is shared between the branches depending on the

resistance.

2.10 describe how current varies with voltage in wires, resistors, metal filament lamps and

diodes, and how this can be investigated experimentally


a) Resistors and wires obey Ohm’s law. Current, I, is proportional to voltage, v, and the graphs are

straight lines which pass through the origin (0,0) of the scales.

b) The filament in a lamp is a metal wire but it gets very hot indeed. The resistance of a metal increases

with temperature – the graph curves when the lamp reaches its working current and temperature.

c) Diodes have a very large resistance when voltage is applied in the ‘wrong’ direction – this is shown by

the horizontal line when the voltage is negative. When the voltage is in the ‘right’ direction (forward

biased), when it reaches around 0.7v, the resistance drops to a small value – the graph curves and

become very steep.

Experiment: To investigate how current varies with voltage. (Ohm’s law)

The resistance of a component is related to the current through it and the voltage across it by the

equation V = I x R. If we wish to find the resistance of a component, this equation can be rearranged to

give R = V/I. The circuit in Figure can be used to investigate this relationship for a piece of resistance

wire.

When switch S is closed for the readings on the ammeter and voltmeter are noted. The value of the

variable resistor is then altered and a new pair of readings taken from the meters. The whole process is

repeated at least six times, the results are placed into a table and a graph of current against voltage is

drawn.

Current, I (A) Voltage, V (v)

0.0 0.0

0.1 0.4

0.2 0.8

0.3 1.2

0.4 1.6

0.5 2.0


The graph in Figure is a straight line passing through the

origin. This tells us that the current flowing through the

wire is directly proportional to the voltage applied across

its end – that is, if the voltage across the wire is doubled

the current flowing through it doubles.

2.11 describe the qualitative effect of changing resistance on the current in a circuit

R α 1/I

Resistance is inversely proportional to current. Higher resistance means lower current and higher

current means lower resistance. In other words resistance is the opposition of current. Resistance blocks

charge flow.

2.12 describe the qualitative variation of resistance of LDRs with illumination and of

thermistors with temperature

Light Dependant Resistors: An LDR is a light dependant resistor. Its

resistance changes with the intensity of light. In dark condition LDRs

contain few free electrons and so have a high resistance. If however

light is shone onto an LDR more electrons are freed and the resistance

decreases. LDRs are often used in light sensitive circuits in devices such

as photographic equipment, automatic lightning controls and burglar

alarms.

Thermistor: A thermistor is a temperature dependant resistor. It

is made from a semiconducting material such as silicon or

germanium. At room temperature the number of free electrons is

small and so the resistance of a thermistor is large. If however if it

is warmed the number of the electrons increases and its

resistance decreases. Thermistors are often used in temperature-

sensitive circuits in devices such as fire alarms and thermostats.


2.13 know that lamps and LEDs can be used to indicate the presence of a current in a circuit

A light-emitting diode (LED) is a special kind of diode that glows

when electricity passes through it. Most LEDs are made from a

semi-conducting material called gallium arsenide phosphide.

LEDs can be bought in a range of colours. They can also be

bought in forms that will switch between two colours (bi-

colour), three colours (tri-colour) or emit infra-red light.

In common with all diodes, the LED will only allow current to

pass in one direction. The cathode is normally indicated by a flat

side on the casing and the anode is normally indicated by a

slightly longer leg. The current required to power an LED is

usually around 20 mA.

2.14 know and use the relationship between voltage, current and resistance:

voltage = current × resistance

V = I × R

2.15 understand that current is the rate of flow of charge

The size of an electric current indicates the rate at which charge flows. Charge(Q) is measured in

coulombs (C). Current is measured in amperes (A). If 1 C of charge flows along a wire every second the

current passing the wire is 1A.

2.16 know and use the relationship between charge, current and time:

charge = current × time

Q = I × t

2.17 know that electric current in solid metallic conductors is a flow of negatively charged

electrons


Current is the flow of charge. One coulomb of charge is equivalent of the charge carried by

approximately six million, million, million (6 x 1018) negative electrons.

Charge direction when connected to a battery

In conductors some electrons are free to drift. But the number of electrons flowing in any one direction

is roughly equal to the number flowing in the opposite direction. There is therefore no overall flow of

charge. However, if a cell or battery is connected across the conductor, more of the electrons now flow

in the direction away from the negative terminal and towards the positive terminal, than in the opposite

direction. There is now a net flow of charge.

Electrons/charges move from the negative terminal to positive. But when you are dealing with topics

such as circuit and motors, it is still considered that current flow from positive to negative. This is called

conventional current.

2.18 understand that:

voltage is the energy transferred per unit charge passed

the volt is a joule per coulomb.

As the charges flow around a circuit, the energy they carry is converted into other forms of energy by

the components they pass through. The voltage across each component tells us how much energy it is

converting. If the voltage across a component is 1v, this means that the component is changing 1J of

electrical energy into a different kind of energy each time 1C of charge passes through it.

d) Electric charge

2.19 identify common materials which are electrical conductors or insulators, including

metals and plastics

Conductors: Electrical conductors are materials that allow current to pass through them. Conductors

have free electron diffusion to pass current. Metals like copper, silver, aluminium have free electrons

and can conduct electricity.

Insulators: Insulators do not conduct electricity because they don’t have free electrons. Examples of

insulators are plastics, rubber, wood etc.

2.20 describe experiments to investigate how insulating materials can be charged by

friction

Experiment: To investigate how insulating materials can be charged by friction


Apparatus: Glass rod, silk cloth, electroscope

Procedure:

1. Take a glass rod and silk cloth.

2. Rub the rod with the cloth.

3. Now, take any of the two materials near the metal plate of an electroscope.

Observation

1. You will notice that the leaf below will deflect.

2. This will prove that charge can be produced by friction.

2.21 explain that positive and negative electrostatic charges are produced on materials by

the loss and gain of electrons

If two materials are rubbed together electrons will be transferred. The one that gains electrons will be

negatively charged and the one that losses electrons will be positively charged.

Materials Positive charge Negative charge

Glass rod rubbed with silk glass Silk

Ebonite rod rubbed with fur fur ebonite

Perspex ruler rubbed with woolen

Perspex Duster

Plastic comb rubbed with hair hair Plastic comb

Polythene strip rubbed with woolen duster

duster Polythene

Cellulose acetate rubbed with woolen duster

acetate duster


2.22 understand that there are forces of attraction between unlike charges and forces of

repulsion between like charges

Similar charges repel each other and unlike charges attract each other. The attraction and repulsion

occurs because of electrostatic force.

Experiment: To investigate unlike charge attracts

Apparatus:

Two pieces of glass rods.

One piece of silk cloth

Insulating thread.

Diagram:

Procedure:

1. Two glass rods are rubbed by silk cloth. The rods become positively charged and the cloth

becomes negatively charged.

2. One positive charged glass rod is hung by an insulating thread.

3. Another positively charged glass rod is approached towards the hung rod.


Observation:

We will see that the hung rod move away.

Conclusion:

Like charges repels.

Experiment: To investigate that like charge repels.

Apparatus:

One piece of glass rod

One piece of ebonite rod

Two pieces of silk rod

Insulating thread.

Diagram:


Procedure:

1. Two silk clothes are taken. When the glass rod is rubbed with the silk cloth, the glass rod

becomes positively charged. Again, when with another silk cloth, the ebonite rod is rubbed, it

becomes negatively charged.

2. The positively charged glass rod is hung by an insulating thread.

3. The negatively charged ebonite rod is approached towards the hung rod.

Observation:

We will see the hung rod moves towards the glass rod.

Conclusion:

Unlike charges attract.

Experiment: Showing that a charged object can attract an uncharged object

If you charge a balloon by rubbing it against your jumper or your hair and then hold the balloon against

a wall, you will find that the balloon sticks to the wall. There is an attraction between the charged

balloon and the uncharged wall.

After the balloon has been charged with static electricity, but before it is brought close to the wall, the

charges will be distributed. The balloon is negatively charged and the wall is uncharged – that is, the

equal numbers of positive and negative charges.

As the negatively charged balloon is bought closer to the wall some of the negative electrons are

repelled from the surface of the wall. This gives the surface of the wall a slight positive charge that

attracts the negatively charged balloon.

2.23 explain electrostatic phenomena in terms of the movement of electrons


An electrostatic phenomenon is an event where electricity has a special effect, for example a static

shock. Electrons move from one material to another. Materials with a negative charge will look for some

way to earth like clouds through lightning.

2.24 explain the potential dangers of electrostatic charges, eg when fuelling aircraft and

tankers

In some situations the presence of static electricity can be a disadvantage.

As aircraft fly through the air, they can become charged with static electricity. As the charge on

an aircraft increases so too does the potential difference between it and earth. With high

potential differences her is the possibility of charges escaping to the earth as a spark during

refueling, which could cause an explosion. The solution to this problem is to earth the plane

with a conductor as soon as it lands and before refueling commences. Fuel tankers that

transport fuel on roads must also be earthed before any fuels is transferred to prevent sparks

causing a fire or explosion.

Television screens and computer monitors become charged with static electricity as they are

used. The charges attract light uncharged particles-that is dust.

Our clothing can, under certain circumstances become charged with static electricity. When we

remove the clothes there is the possibility of receiving a small electric shock as the charges

escape to the earth.

Workers handing electronic components must take care not to become charged by static as this

can easily destroy expensive components. They wear earthing straps and work on earthed metal

benches to prevent this.

2.25 explain some uses of electrostatic charges, eg in photocopiers and inkjet printers.

Electrostatic charges can be used in electrostatic paint spraying, inkjet printers, photocopiers,

electrostatic precipitators etc.

Electrostatic paint spraying

Painting an awkwardly shaped object such as bicycle frame with a spray can be very time consuming and

very wasteful of paint. Using Electrostatic spraying can be the process efficient.


Let the metal spray nozzle be connected to a positive terminal so the paint that emerges will be positive

charged. The bicycle frame should be connected to a wire and it will become negatively charged. The

positively charged paint will be attracted to the frame. There is the added benefit that paint is attracted

into places, such as tight corners that might otherwise not receive good coating.

Inject Printers

Many modern printers use inkjets to direct a fine jet of ink drops onto paper. Each spot of ink is given a

charge so that as it falls between a pair of deflecting plates, electrostatic forces direct it to the correct

position. The charges on the plates change hundreds of times each second so that each drop falls in a

different position, forming pictures and words on the paper as required.

Photocopiers


In photocopiers, the paper is shone in bright light which reflects to a rotating drum. The dark writings

and pictures do not reflect. As a result the light removes the charges in the drum. Carbon powder

attaches to the charges in the drum and the pictures and writings are pasted into a sheet of paper.

Electrostatic precipitators

Many heavy industrial plants, such as steel-making furnaces and coal fired power stations, produce large

quantities of smoke. This smoke carries small particles of ash and dust into the environment, causing

health problems and damage to buildings. One way of removing these pollutants from the smoke is to

use electrostatic precipitators.


As the smoke initially rises up the chimney, it passes through a mesh of wires that are highly charged. As

they pass through the mesh, the ash and dust particles become negatively charged. Higher up the

chimney these charged particles are attracted by and stick to large metal earthed plates. The cleaner

smoke is then released into the atmosphere. When the earthed plates are completely covered with dust

and ash, they are given a sharp rap. The dust and ash fall into collection boxes, which are later emptied.


Section 3: Waves

a) Units

3.1 use the following units: degree (°), hertz (Hz), metre (m), metre/second (m/s), second

(s).

Unit of an angle: degree (o)

Unit of frequency: hertz (Hz)

Unit of distance or wavelength: metre (m)

Unit of speed/velocity: metre/second (m/s)

Unit of time-period: second (s)

b) Properties of waves

3.2 understand the difference between longitudinal and transverse waves and describe

experiments to show longitudinal and transverse waves in, for example, ropes, springs and

water

Waves can transfer energy and information from one place to another without transfer of matter.

Waves can be divided into two types: mechanical waves and electromagnetic waves.

Mechanical waves can be of two types: transverse and longitudinal.

Transverse waves: A transverse wave is one that vibrates or oscillates, at right angles to the direction in

which the energy or wave is moving. Example of transverse waves include light waves and waves

travelling on the surface of water.

Longitudinal waves: A longitudinal wave is one in which the vibrations or oscillations are along the

direction in which the energy or wave is moving. Examples of longitudinal waves include sound waves.

Transverse wave don’t need medium to move. Longitudinal wave needs medium to move.

Experiment: To show different types of waves in spring.

Transverse –


If you waggle on end of a slinky spring from side to side you will see waves travelling through it. The

energy carried by these waves moves along the slinky from one end to the other, but if you look closely

you can see that the coils of the slinky are vibrating across the direction in which the energy is moving.

This is an example of transverse wave.

Longitudinal –

If you push and pull the end of a slinky in a direction parallel to its axis, you can see energy travelling

along it. This time however the coil of the slinky are vibrating in direction that are along its length. This is

an example of longitudinal wave.

Experiment: To create water waves using a ripple tank


When the motor is turned on the wooden bar vibrates creating a series of ripples on the surface of

water. A light placed above the tank creates pattern of the water waves on the floor. A light placed

above the tank creates patterns of the water waves on the floor. By observing the patterns we can see

how the water waves are behaving.

3.3 define amplitude, frequency, wavelength and period of a wave

Amplitude: Amplitude is the maximum displacement of a part of the medium from its rest position.

Wavelength: The distance between a particular point on a wave and the same point on the next wave

(for example, from crest to crest) is called the wavelength (λ).

Frequency: The number of waves produced each second by a source, or the number passing a particular

point each second is called frequency ( f).

Period: The period of a wave is the time for one complete cycle of the waveform.


Experiment: Adjusting ripple tank to investigate wavelength and frequency

The motor can be adjusted to produce a small number of waves each second. The frequency of the

waves is small and the pattern shows that the waves have a long wavelength.

At higher frequencies, the water waves have shorter wavelengths. The speed of the waves does not

change.

Experiment: Demonstrating refraction using ripple tank

Refraction, the bending of light waves as they pass from one material to another, can be demonstrated

by reducing the depth of water in the ripple tank (with a transparent glass or plastic sheet). Ripples

travel more slowly if the depth of the water in the ripple tank is smaller. When setting up a ripple tank it

is therefore important that the tank is level. Another problem with ripple tanks is unwanted reflection

from the sides of the tank; these result in pretty patterns but make analysts of what you see very

difficult. Most ripple tanks have sloping sides to reduce unwanted reflections.

Experiment: To demonstrate diffraction using vibrating bar

To show the interesting effects of diffraction you need to set up continuous plane wavefronts and

(circular wavefronts respectively). This is done with a vibrating bar placed wither directly in contact with

the water or with two dippers just touched the water for circular wavefronts. The frequency of vibration

is controlled frequency of the waves is controlled by varying the speed of electric motor attatched to the

beam.


3.4 understand that waves transfer energy and information without transferring matter

Waves are means of transferring energy and information from place to place. These transfers take place

with no matter being transferred. Mobile phones, satellites etc. rely on waves.

Example: If you drop a large stone into a pond, waves will be produced. The waves spread out from the

point of impact, carrying to all parts of the pond. But the water in the pond does not move from the

centre to the edges.

3.5 know and use the relationship between the speed, frequency and wavelength of a wave:

3.6 use the relationship between frequency and time period

3.7 use the above relationships in different contexts including sound waves and electromagnetic

waves

As all wave share properties the above relations can be used for any type of wave.

P – 1: The period of a wave is 0.01 second. What is its frequency?

Ans: Frequency = 1/T

= 1/0.01s

= 100 Hz


P – 2: The frequency of a wave is 250 Hz and the wavelength is 0.02m. What is speed of the wave?

Ans:

= 250 Hz x 0.02s

= 5 m/s

3.8 understand that waves can be diffracted when they pass an edge

Diffraction is the slight bending of waves as it passes around the edge of an object. The amount of

bending depends on the relative size of the wavelength of light to the size of the opening. If the opening

is much larger than the wave's wavelength, the bending will be almost unnoticeable. However, if the

two are closer in size or equal, the amount of bending is considerable.

3.9 understand that waves can be diffracted through gaps, and that the extent of diffraction

depends on the wavelength and the physical dimension of the gap.

Diffraction involves a change in direction of waves as they pass through an opening or around a barrier

in their path. Water waves have the ability to travel around corners, around obstacles and through

openings. This ability is most obvious for water waves with longer wavelengths. Diffraction can be

demonstrated by placing small barriers and obstacles in a ripple tank and observing the path of the

water waves as they encounter the obstacles. The waves are seen to pass around the barrier into the

regions behind it; subsequently the water behind the barrier is disturbed. The amount of diffraction (the

sharpness of the bending) increases with increasing wavelength and decreases with decreasing

wavelength. In fact, when the wavelength of the waves is smaller than the obstacle, no noticeable

diffraction occurs.


c) The electromagnetic spectrum

3.10 understand that light is part of a continuous electromagnetic spectrum which includes

radio, microwave, infrared, visible, ultraviolet, x-ray and gamma ray radiations and that all

these waves travel at the same speed in free space

The electromagnetic spectrum is a continuous spectrum of waves which includes the visible spectrum.

1) they all transfer energy

2) they are all transverse waves

3) they all travel at speed of light in vacuum (3 x 108 m/s)

4) they can all be reflected, refracted and diffracted

3.11 identify the order of the electromagnetic spectrum in terms of decreasing wavelength

and increasing frequency, including the colours of the visible spectrum

Different frequencies and wavelength differ them into different groups and consequently have different

properties. Radio waves have the lowest frequency and the longest wavelength. Gamma rays have the

highest frequency and the shortest wavelength.

A mnemonic can help: Run Miles In Very Unpleasant eXtreme Games.

Colours of the visible spectrum

There are seven colours in the visible spectrum: red, orange, yellow, green, blue, indigo and violet. Red

has the longest wavelength and lowest frequency.


A mnemonic can help: Richard Of York Gave Battle In Vain

The EM spectrum is continuous – it is only broken upto into distinct zones for convenience. For example,

the visible light spectrum is made up of an indeterminate number of colours that blend smoothly from

on shade to the next.

3.12 explain some of the uses of electromagnetic radiations, including:

Radio waves: It is used in communicating information. This can be speech, radio and television, music

and encoded messages like computer data, navigation signals and telephone conversations. The

properties that make radio waves suitable for communicating are:

Radio waves can travel quickly.

Can code information.

Can travel long distance through buildings and walls.

It is not harmful.

Microwaves: Microwaves are used in microwave oven which cooks food more quickly than in normal

oven. Microwaves are also used in communications. The waves pass easily through the Earth’s

atmosphere and so are used to carry signals to orbiting satellites. From here, the signals are passed on

to their destination. Messages sent to and from mobile phones and radar are also carried by

microwaves.

Infrared: Special cameras designed to detect infra-red waves can be used to create image even in the

absence of visible light. The image can be created because of the different temperatures of objects.

Wavelength of infrared from warm objects is shorter than the infrared from cool objects. Infra-red

radiation is also used in remote controls for televisions, videos and stereo systems. Moreover it is used

in heating materials like heater.

Visible light: The main use of visible light is to see. Visible light from lasers is used to read compact discs

and barcodes. It can also be sent along optical fibres, so it can be used for communication or for looking

into inaccessible places such as inside of the human body. Furthermore, it has uses in photography too.


Ultraviolet: Some chemicals glow when exposed to UV light. This property of UV light is used in security

markers. The special ink is invisible in normal lights but becomes visible in UV light. UV light is also used

in fluorescent lamps, to kill bacteria, to harden fillings and disco ‘black’ lights. Some insects can see into

the ultraviolet part of spectrum and use this to navigate and to identify food sources.

X-rays: X-ray is used to take pictures of patient’s bone to determine any fracture. X-rays are also used in

industry to check the internal structures of objects-for example: to look for cracks and faults in buildings

or machinery- and at airport as part of the security checking procedure. The X-rays produced by

collapsing stars are also used in radio astronomy.

Gamma rays: They are used to sterillise medical instruments, to kill micro-organisms so that food will

keep for longer and to treat cancer using radiotherapy.

3.13 understand the detrimental effects of excessive exposure of the human body to

electromagnetic waves, including:

and describe simple protective measures against the risks.

Microwaves: Micro waves might cause internal heating of body tissue. For this microwave ovens have

metal screens that reflect microwaves and keep them inside the oven. It also has perceived risk of

cancer.

It can be prevented by closing oven doors and using hands-free cell phones.

Infrared: The human body can be harmed by too much exposure to infra-red radiation, which can cause

skin burning and cell damage.

It can be prevented by avoiding hot places, using reflective clothing and avoiding exposure to sun.

Visible light: Visible light can cause eye damage.

It can be prevented by sun glasses and avoiding exposure to the sun.

Ultraviolet: Overexposure of ultraviolet light will lead to sunburn and blistering. This can also cause skin

cancer, blindness and damage to surface cells.

Protective goggles or glasses and skin creams can block the UV rays and will reduce the harmful effects

of this radiation.

X-rays: X-ray has risk of cancer and cell damage.

Lead shielding, Monitor exposure (film badge), protective clothing can be used to prevent the risk.

Gamma rays: Gamma rays can damage to living cells. The damage can cause mutations in genes and can

lead to cancer.

Lead shielding, Monitor exposure (film badge) can be used to prevent the risk.


d) Light and sound

3.14 understand that light waves are transverse waves which can be reflected, refracted

and diffracted

Light waves are transverse wave that is emitted from luminous (objects that emit their own light such as

sun, stars, fires, light bulbs etc.) or reflected from non-luminous objects (objects which do not emit their

own light but are seen by their reflection of light). Light waves are transverse wave and like all waves,

they can be reflected, refracted and diffracted.

3.15 use the law of reflection (the angle of incidence equals the angle of reflection)

The law of reflection states that:

i) The incident ray, reflected ray and normal all lie in the same plane.

ii) The angle of incidence (ϴi) is equal to the angle of reflection (ϴr).

Experiment: To illustrate the laws of reflection.

Apparatus: Ray box, strip of plane mirror, protractor, piece of paper.

Procedure:

1. Set up the apparatus as shown in Figure.


2. Vary the angle of incidence i and measure the angle of reflection r.

3. Compare the values of i and r.

3.16 construct ray diagrams to illustrate the formation of a virtual image in a plane mirror

Types of images:

i. Virtual images: Image through which the rays of light don’t not actually pass is called virtual

image. Example: Image formed in the mirror. Virtual images cannot be produced on a screen.

ii. Real images: Images created with rays of light actually passing through them are called real

images. Example: cinema screen.

Fig. Reflection of a tree. How the virtual image looks like below the lake.

Properties of an image in a plane mirror:

The image is as far behind the mirror as the object is in front

The is the same size as the object

The image is virtual as it appears to be behind the mirror. The rays of light are not actually

coming from the place where the image seems to be.

The image is laterally inverted – that is, the left side and right side of the image appear to be

interchanged.

How to construct ray diagrams?

Things we include in ray diagrams of a plain mirror:

i- Object ii-Observer's eye or some indication iii- Plane mirror iv- Image.

1- Have object infront of the mirror.


2- Draw atleast two rays emanating from the object (one from the top of the object and other at the

bottom as shown below) and going towards mirror-- for some objects we need three or more.

3- Reflect ray from the mirror by using law of reflection towards observer.

4- Extend the rays by dotted lines behind the mirror.

5- Construct the image according to the position of the ray ie if ray is coming from the bottom side of

the object then it would show the bottom side and so and so as shown below.


3.17 describe experiments to investigate the refraction of light, using rectangular blocks,

semicircular blocks and triangular prisms

As a light ray passes from one transparent medium to another, it bends. This bending of light is called

refraction. Refraction occurs due to having different speed of light in different medium. For example,

light travels slower in glass than in air. When ray of light travels from air to glass, it slows down as it

crosses the boundary between two media. The change in speed cause the ray to change direction and

therefore refraction occurs.

The light bends towards the normal as

it passes from low-density to high-

density (air to glass). The light is

refracted and upon emerging from the

glass the light bends away from the

normal as it passes high density to

low-density (glass to air).

When the ray first entered the semi-circular glass, it

was along the normal. As a result, it went straight.

While escaping the glass, the light bend away from

the normal.


Experiment: To demonstrate the refraction of light through a piece of glass block.

Apparatus: Rectangular glass block with one face frosted, two rays boxes, piece of paper.

Procedure:

1. Place the glass block on a piece of paper with the frosted side down.

2. Send two narrow rays of light through the glass block as shown in Figure.

3. Observe the paths of the two rays of light.

4. Vary the angle of incidence i and measure the angle of refraction r.

3.18 know and use the relationship between refractive index, angle of incidence and angle

of refraction:

The ratio between sine of the angle of incidence and the sine of the angle of refraction is called

refractive index. In a material, the refractive index is constant throughout the circuit.

The incident ray entered the prism

and is refracted. This ray travels along

the prism in straight line, then again

refraction after leaving the prism.


i

i

i

i

Lighter mediums means that light can pass easily/ speed of light is more.

Dense/light doesn’t mean physical density rather than optical condition.

Refraction takes place in second medium.

The ratio from a vacuum to a denser medium is called absolute refractive index.

The ratio from a medium to another medium is called relative refractive index.

It doesn’t have a unit because it is the ratio of same curve.

Wavelength decreases in a denser medium, thus decreasing speed.

The higher the wavelength, the more the light will bend.

The higher the wavelength, the less the angle of refraction.

3.19 describe an experiment to determine the refractive index of glass, using a glass block

Experiment: To determine the refractive index of glass, using a glass block.

i. Put the glass block on an wooden table which is passed by a white sheet.

ii. The border of the block is marked by a pencil.

iii. At one border draw a normal and draw three lines to use as incident ray.

iv. Set a ray box through anyone of the lines.

v. The ray travels and passes through the glass block and finally emerges from the glass block.


vi. The passage of the ray is marked by putting some pins.

vii. Now move the glass block and gain the footprints of the pins to show the passage of the ray.

viii. Now using a protractor measure the ∠i and ∠r.

ix. Now using,

; calculate refractive index.

Ways to improve result:

1. Repeat the experiment, and find the average reading.

2. Plot a graph of sin I against sin r and find the gradient.

3. Vary the value of i and repeat.

3.20 describe the role of total internal reflection in transmitting information along optical

fibres and in prisms

Total internal reflection: When light falls on the surface of a lighter medium from denser medium at an

angle of incidence greater than critical angle, then the light does not refracts. It rather reflects in the

self-medium. This type of reflection is called total internal reflection.

Condition of total internal reflection:

1. Light should fall in the surface of lighter medium from denser medium.

2. Angle of incidence must be greater than the critical angle.

Uses of total internal reflection:

i) The prismatic periscope


Light passes normally through the surface AB of the first prism (that is, it enters the prism at 90o) and so

is undeviated. It then strikes the surface AC of the prism at angle of 45o. The critical angle for glass is 42o

so the ray is totally internally reflected and is turned through 90o. On emerging from the first prism the

light travels to a second prism which is positioned such that the ray is again totally internally reflected.

The ray emerges parallel to the direction in which it was originally travelling.

The final image created by this type of periscope is likely to be sharper and brighter than that produced

by a periscope that uses two mirrors. Because in mirrors, multiple images are formed due to several

partial internal reflections at the non-silvered glass surface of the mirror.

ii) Reflectors

Reflector is a block of glass that changes the direction of rays into the required position.


Light entering the prism undergoes total internal reflection twice. It emerges from prism travelling back

in the direction from which it originally came. This arrangement is used in bicycle reflectors and

binoculars.

iii) Optical fibres

Optical fibre uses the property of total internal reflection. This is very thin strand composed of two

different types of glass. The inner core is more optically dense than the outer one. As the fibres are

narrow, light entering inner core always strike the boundary of the two glasses at an angle greater than

critical angle. This technique is used to send information very fast at the speed of light.

Optical fibres are also used in endoscopes and telecommunications.

The endoscope is used by doctors to see inside human body. Light travels down one bundle of fibres and

illuminates the object to be viewed. Light reflected by the object travels up a second bundle of fibres. An

image of object is created by the eyepiece.

Modern telecommunication systems use optical fibres to transmit messages. Electrical signals from a

telephone are converted into light energy by tiny lasers, which send pulses of light into the ends of


optical fibres. A light-sensitive detector at the other end changes the pulses back into electrical signals,

which then flow into a telephone receiver.

Optical fibres allow a much wider bandwidth. This means that many different digital signals can share

the same optical fibre, so much more information can be transmitted along an optical fibre than by

using an analogue signal.

Advantages of sending data using Optical Fibre:

Optical fibre is less prone to noise.

It is less prone to heating.

It can send more information per second than copper wires.

3.21 explain the meaning of critical angle c

Critical angle is an incident angle at which the incident ray is refracted and the refracted angle is equal

to 90 degree in condition that the light falls on the surface of a lighter medium from denser medium.

3.22 know and use the relationship between critical angle and refractive index:

i

i

3.23 understand the difference between analogue and digital signals

To send a message using a digital signal, the information is converted into a sequence of numbers called

a binary code. Digital electrical signals can either have of only two possible values (typically 0v and 5v).

These represent the digits 0 and 1 used in the binary number system.

In the analogue method, the information is converted into electrical voltages and current that vary

continuously.


3.24 describe the advantages of using digital signals rather than analogue signals

i. Regenerating digital signal creates a clean accurate copy of the original signal but analogue

signal are corrupted by other signals.

ii. With digital signal, you can broadcast programs over the same frequency. It is possible because

digital signals can carry more information per second than analogue signals. In analogue signal

you need wider range of frequency to broadcast.

iii. Digital systems are generally easier to design and build than analogue systems. That is the

information can be stored and processed by computers.

3.25 describe how digital signals can carry more information

Digital signals are capable of carrying more information than analogue signals because digital signals

make use of the bandwidth more efficiently by closely approximating the original analogue signal. The

parts of the signal that do not carry any information are thrown out thus saving the bandwidth from

being used needlessly. Also, depending on the coding process, digital signals are much more efficient at

filtering out noise than are analogue signals, which do not filter out noise at all thus saving even more

bandwidth. The process of approximating the analogue signal in digital signal processing is called

quantization.

3.26 understand that sound waves are longitudinal waves and how they can be reflected,

refracted and diffracted

Sound waves are longitudinal waves. They are produced by vibration of objects.Like other waves they

can also be reflected refracted and diffracted.

Reflection:

Sound waves reflect when they bounce back from a surface so that the angle of incident is equal to the

angle of reflection. A reflected sound wave is called an echo.

Example:


Sound is produced behind a nearby wall. After few seconds, a second sound is heard. Due to the

reflection of sound wave echo is heard.

Refraction:

Sound waves refract when it changes direction while travelling across a high dense medium.

Example:

Sound wave is sent from the boat to determine the depth of the sea. If refracts when it enters into

water. The return wave is received by a receiver. Measure the time required we can measure the depth

of sea.

Diffraction:

Sound waves are diffracted when they spread while travelling through a narrow space such as doorway.

Example:


Sound is produced in the corridor. When it leaves the corridor, it diffracts. So a person standing at one

side can hear the sound.

How sound wave travels?

When a vibration occurs, it pushes the air molecules around it closer together. This creates a

compression. These particles then push against neighbouring particles so that the compression appears

to be moving. Behind the compression is a region where the particles are spread out. This region is

called rarefaction. In this way, they create compression and rarefaction and transfer energy.

3.27 understand that the frequency range for human hearing is 20 Hz – 20,000 Hz

An average person can only hear sound that have a frequency higher than 20Hz but lower than 20000

Hz. This spread of frequency is called audible range. Frequency higher than 20000 Hz which cannot be

heard by humans are called ultrasounds. Frequency lower than 20 Hz that cannot be heard by humans

are called infrasound.

3.28 describe an experiment to measure the speed of sound in air

Experiment: To measure the speed of sound by direct method


Apparatus: Starting pistol, stopwatch, measuring tape.

Procedure:

1. By means of measuring tape, observers are positioned at known distance apart in an open field.

2. First observer fires a starting pistol.

3. Second observer seeing the flash of the starting pistol, starts the stopwatch and then stops it

when he hears the sound. The time interval is then recorded.

Ways to improve:

1. Repeat the experiment a few times and compute the values of the speed of sound for each

experiment. Find the average value. This procedure minimizes random errors in finding the time

interval between seeing the flash and hearing the sound.

2. Observers exchange positions and repeat experiment. This procedure will cancel the effect of

wind on the speed of sound in air.

Experiment: To measure the speed of sound using echoes

One boy claps, the sound travels and reflects from a nearby wall. After few seconds the echo is heard.

Another boy starts the stopclock when the sound is produced and stopped the clock when the echo is

heard. Now if the distance between the source of sound can reflector is d1 and the speed of sound will

be

; where t = time from go and back.

Sources of error:

i. Reaction time, i.e when starting the clock by hearing the echo or stopping it when receiving the

echo.

Ways to improve:

i. Repeat this 5 times.


ii. Make sure there are no other large reflection surfaces nearby.

Experiment: To measure the speed of sound using resonance tubes and tuning forks

A resonance tube is a Perspex tube with a water reservoir. The height of the water in

the tube can be adjusted to change the length of the tube, as the sound waves will

be reflected at the water surface. A sound of a known frequency is made by striking

a tuning fork and holding it above the open end of the tube. The water column is

adjusted until the loudest sound can be heard. As in the figure, the first resonance

will be heard when the length of the air in the tube is equal to a quarter of the

wavelength. You can check your result by lowering the water level to find the next

resonance, at ¼ of the wavelength. The speed of sound I then calculated using

Experiment: To measure the speed of sound using oscilloscopes

The apparatus is set up as in the figure. Set the signal generator to give a sound with frequency of about

1kHz. Start with the microphones close together, and observe how the two traces on the oscilloscope

compare. Then move one microphone further away from the loudspeaker until it is one complete

wavelength away from the first – you know you have arrived at this point when the traces one the

oscilloscope screen are exactly above one another. Measure the distance between the microphone to

get the wavelength of the sound, and use the oscillioscope screen to find an accurate value for the

frequency. The speed of sound can then be worked out using the formula .

3.29 understand how an oscilloscope and microphone can be used to display a sound wave

When sound waves enter the mircrophone, they make a crystal or a metal plate inside it vibrate. The

vibrations are changed into electrical signals, and the oscilloscope uses these to make a spot which

moves up and down on the screen. It moves the spot steadily sideways at the same time, producing a

wave shape called waveform.

The waveform is really a graph showing how the air pressure at the microphone varies with time. It is

not a picture of the sound waves themselves: Sound waves are not transverse (up and down).

Oscilloscopes are instruments used to show waveforms of electrical signals.


When we speak in microphone, sound waves are converted into electrical signals. When we connect the

microphone to the oscilloscope then the oscilloscope would display waveforms onto the screen. The

waveforms are a representation of sound waves.

.

3.30 describe an experiment using an oscilloscope to determine the frequency of a sound

wave

Experiment: To determine the frequency of a sound wave

i. Sound is produced by a loudspeaker.

ii. The microphone catches the sound and transmits it into electrical signal.

iii. The electrical signal is feed to the oscilloscope.

iv. The oscilloscope displays the electrical signal as wave pattern.

v. The time base knob is adjusted for value 5 ms per division.

vi. Now count the number of division occupied by one cycle of the wave.

vii. Calculate the time for one cycle (T).

viii. Now, frequency,

3.31 relate the pitch of a sound to the frequency of vibration of the source

The sharpness or drollness of a sound is called its pitch.


The more something vibrates the higher frequency.

The higher frequency, the higher pitch.

So the more vibrations the higher pitch.

3.32 relate the loudness of a sound to the amplitude of vibration.

The bigger the vibration the higher the amplitude.

The higher the amplitude the louder the sound.


Section 4: Energy resources and energy transfer

a) Units

4.1 use the following units: kilogram (kg), joule (J), metre (m), metre/second (m/s),

metre/second2 (m/s2), newton (N), second (s), watt (W).

Unit of mass: kilogram(kg)

Unit of energy: joule(J)

Unit of distance: metre(m)

Unit of speed or velocity: metre/second (m/s)

Unit of acceleration: metre/second2 (m/s)

Unit of force: newton (N)

Unit of time: second (S)

Unit of power: watt(W)

b) Energy transfer

4.2 describe energy transfers involving the following forms of energy: thermal (heat), light,

electrical, sound, kinetic, chemical, nuclear and potential (elastic and gravitational)

Thermal energy: The energy which is released by a hot object when it cools down is called thermal

energy. E.g: If we rub our hands together, kinetic energy will transform into thermal energy.

Light energy: The energy which is released from luminous object is called light energy. E.g.: In a filament

lamp, electrical energy is converted to heat energy and light energy.

Electrical energy: The energy of charged object is called electrical energy. E.g.: In an electric generator,

kinetic energy is converted to heat and electrical energy.

Sound energy: The energy by which we can hear is called sound energy. E.g.: Clapping our hands will

convert kinetic energy to sound and little amount of heat energy.

Kinetic energy: The energy of a moving object is called kinetic energy. E.g.: In a ceiling fan, electrical

energy is converted to kinetic energy.

Chemical energy: The energy which is released by chemical reaction is called chemical energy. E.g: In a

motor car, chemical energy is converted to heat, electrical and kinetic energy.

Nuclear energy: The energy which is released by nuclear reaction is called nuclear energy. E.g.: Energy is

nuclear power stations.

Potential energy: The energy which is gained by changing size, shape and position of an object is called

potential energy. E.g: Raise a ball 10m above ground, it will gain gravitational potential energy.


4.3 understand that energy is conserved

Energy is not created or destroyed in any process. It is just converted from one from type to another.

Wasted energy: When we try to do things, there is some energy converted to unwanted forms. This

form of energy is known as wasted energy.


Effeciency is the ratio of useful energy output and the total energy input.

4.5 describe a variety of everyday and scientific devices and situations, explaining the fate

of the input energy in terms of the above relationship, including their representation by

Sankey diagrams

Whenever we are transferring energy, proportion of input energy is wasted. Like a lamp has input

energy of 100J. It uses 10J to give light and the other 90J is wasted as heat.

In a Sankey diagram it is presented like this:


4.6 describe how energy transfer may take place by conduction, convection and radiation

There are three basic ways energy can transfer from place to place: conduction, convection and

radiation.

Conduction: Thermal conduction is the transfer of heat energy through substance mainly metals,

without the substance itself moving. They transfer energy through molecular vibration or free electron

diffusion.

Metals are good conductors of heat but non-metals and gases are usually poor conductors of heat. Poor

conductors are called insulators. Heat energy is conducted from the hot end of an object to the cold

end.

Heat conduction in metals

The electrons in piece of metal can leave their atoms and move about in the metal as free electrons. The

parts of the metal atoms left behind are now charged metal ions. The ions are packed closely together

and they vibrate normally continually. The hotter the metal, the more kinetic energy these vibration

have. The kinetic energy is transferred from hot parts of the metal to cooler parts by the free electrons.

These move through the structure of the metal, colliding with ions as they go.

Convection: Convection is the transfer of energy by means of fluids (liquids or gases) by the upward

movement of warmer, less dense region of fluid.

The particles in fluids can move from place to place. Convection occurs when particles with a lot of heat

energy in a liquid or gas move and take the place of particles with less heat energy in a liquid or gas

move and take the place of particles with less heat energy. Heat energy is transferred from hot places to

cooler places by convection.

Liquids and gases expand when they are heated. This is because the particles in liquids and gases move

faster when they are heated than they do when they are cold. As a result, the particles take up more

volume. This is because the gap between particles widens, while the particles themselves stay the same

size.

The liquid or gas in hot areas is less dense than the liquid or gas in cold areas, so it rises into the cold

areas. The denser cold liquid or gas falls into the warm areas. In this way, convection currents that

transfer heat from place to place are set up.

Radiation: Radiation is the transfer of energy by means of wave (Infra-red). It doesn’t need any medium

to flow through. It travels at the speed of light and is actually a specific part of this family of

electromagnetic waves. So radiation is the continual emission of infrared waves from the surface of all

bodies transmitted without the aid of medium.

4.7 explain the role of convection in everyday phenomena

1. Household hot-water systems


The working principle of the household hot-water system which is based on the convection in liquids is

as follows:

Water is heated in the boiler by gas burners. The hot water expands and becomes less dense. Hence, it

rises and flows into the upper half of the cylinder.

To replace the hot water, cold water from the cistern falls into the lower half of the cylinder and then

into the boiler due to the pressure difference.

The overflow pipe is attached to the cylinder just in case the temperature of the water becomes too

high and causes a large expansion of the hot water.

The hot-water tap which is led from the overflow pipe must be lower than the cistern so that the

pressure difference between the cistern and the tap causes the water to flow out of the tap.

2. Electric kettles.

The heating coil of an electric kettle is always placed at the bottom of the kettle.

When the power is switched on, the water near the heating coil gets heated up, expands and becomes

less dense. The heated water therefore rises while the cooler regions in the upper part of the body of

water descend to replace the heated water.

3. Air-conditioners

The rotary fan inside an air-conditioner forces cool dry air out into the room. The cool air, being denser,

sinks while the warm air below, being less dense, rises and is drawn into the air-conditioner where it is

cooled. In this way, the air is recirculated and the temperature of the air falls to the value preset on the

thermostat.

4. Refrigerators

Refrigerators work in very much the same way as air-conditioners. The freezing unit is placed at the otp

to cool the air so that the cold air, being denser, sinks while the warm air at the bottom rises. This sets

up convection currents inside the cabinet which help to cool the contents inside.


4.8 explain how insulation is used to reduce energy transfers from buildings and the human

body.

The bigger the difference in temperature between an object and its surroundings, the greater the rate at

which heat energy is transferred. Other factors also effect the rate at which an object transfers energy

by heating. These include the:

Surface area and volume of the object.

If we compare two objects of the same mass and made of same material, but having different

surface areas, the object with the larger surface area will emit infra-red radiation at a higher

rate.

Material used to make the object.

A conductor conducts heat away more quickly than a insulator. The better its conductivity, the

faster it will release heat.

Colour and texture of the surface

Dull, black surfaces are better emitter of infrared radiation than shiny, white surfaces.

Surface temperature

The rate of transfer of energy by radiation also depends on the surface temperature. The higher

the temperature of the surface of the object relative to room temperature, the higher the rate

of energy transfer.

Energy efficient houses and insulation

Reduce heat transfer by conduction:

Use a vacuum: Conduction needs matter; used in vacuum flasks, some types of double glazing

etc.

Use air: Air is a good insulating material. Many materials like wool, feathers, furs etc. trap air so

it cannot circulate. This works because air is a very poor conductor of heat. Houses use fibre


glass insulation and cavity walls are sometimes filled with a foam (again, to stop circulation by

convection).

Use water: Wetsuits trap a layer of water around the body because water is a poor conductor.

Reduce heat transfer by convection:

Use a vacuum: Convection needs gases or liquids, used in vacuum flasks, some types of double

glazing, etc.

Use trapped gas or liquid. This restricts circulation, which is necessary for convection to occur.

The size of gap between the sheets of glass is a compromise. A narrow gap makes the effect of

convection smaller, but it allows a greater amount of heat transfer by conduction.

Reduce heat transfer by radiation:

Use shiny surfaces: Very shiny surfaces reflect (heat) radiation well. Fire fighters wear shiny suits

to stop heat radiation getting to their bodies. Shiny surfaces are also poor radiators of heat.

Space blankets, for example, retain the body heat of athletes or hill-walkers suffering from

exposure. This is because they have a shiny inner surface which reflects heat back to the person

and also a shin outer surface which is a poor radiator of infrared.

Other measures:

Thermostats and computer control systems for central heating can further reduce the heating

needs of a house. They stop rooms being heated too much by switching off the heat when a

certain temperature is reached.

Reduction or elimination of draughts from poorly fitting doors and windows.

c) Work and power

4.9 know and use the relationship between work, force and distance moved in the direction

of the force:

Energy is the ability to do work.

1J of work is done when a force of 1N is applied through a distance of 1m in the direction of the force.

4.10 understand that work done is equal to energy transferred

Doing work means the energy is either decreased or increased. If a weight of 500N is raised 2m, 1000J of

work is done. That means energy is increased by 1000J. Therefore work done is equal to energy

transferred.


The energy that the weight has gained is called gravitational potential energy.



Kinetic energy = ½ x mass x velocity2

K.E = ½ x m x v2

4.13 understand how conservation of energy produces a link between gravitational

potential energy, kinetic energy and work

An object of mass, m weights m x g newtons. So the force, F, needed to lift is mg. If we raise the object

through a distance h, the work done on the object is mgh. This is also the gain of GPE.

When the object is raised, it falls-it loses GPE but gains KE. At the end of the fall, all the initial GPE is

converted into KE. And that’s how energy is conserved.

4.14 describe power as the rate of transfer of energy or the rate of doing work

Power is the rate of transferring energy or doing work. Its measures how fast energy is transferred. The

Watt is the rate of transfer of energy of one joule per second.

4.15 use the relationship between power, work done (energy transferred) and time taken:

d) Energy resources and electricity generation

4.16 describe the energy transfers involved in generating electricity using:

Wind: Winds are powered by the Sun's heat energy. Wind is a renewable source of energy.

Wind mills have been used to grind corn and power machinery like pumps drain lowland areas.

Today, wind turbines drive generators to provide electrical energy. Here, kinetic energy is

transformed to electrical energy.

Water: Water is used to generate energy in three ways: Hydroelectric power, Tidal power &

Wave energy. All the ways uses the same role using the movement of water (K.E.) to rotate that

generator and produce electricity. In this case kinetic energy is also transformed to electrical

energy.

Geothermal resources: Geothermal energy is heat energy stored deep inside the Earth. The

heat in regions of volcanic activity was produced by the decay of radioactive elements. The

heated water from the earth’s crust is used to rotate turbines in generator. Here, heat energy is

converted to kinetic energy which is converted to electrical energy.


Solar heating systems: Solar heating panels absorb thermal radiation and use it to heat water.

The panels are placed to receive the maximum amount of the Sun’s energy. This produce steam

which can be used to drive electricity generators.

Solar cells: Solar energy directly converts light energy into electrical energy.

Fossil fuels: Fossil fuels are natural gas, oil and coal. Those are burned which rotates the turbine

in the generator to produce electricity.

Nuclear power: Nuclear fuels like uranium are used in nuclear generator. The heat produced in

nuclear reaction is used to produce steam from water which rotates the turbine and produce

electricity.

4.17 describe the advantages and disadvantages of methods of large- scale electricity

production from various renewable and non- renewable resources.

Renewable Resources:

Advantages Disadvantages

Wind energy

Relatively cheap to set up

Clean – no waste products

Relatively efficient at converting energy into electricity

Only produce energy when it is windy

Can be used only in certain places

Can be an eyesore

Can produce noise pollution

May kill birds and bats

Wave energy

Continuously available

Clean - no waste products

Moderately efficient

Expensive to set up

Only suitable in certain locations

Tide energy



Efficient

Damaging to environment

Expensive to set up

Only suitable in certain geographical locations

Solar energy

Clean-no waste products Expensive in terms of amount of energy produced

Not very efficient method

Energy supply is not continuously available

Best suited to climates with low amounts of cloud cover

Geothermal energy

Clean- no waste products

Can provide direct heating as well as heat/steam to drive electricity generators

Moderate start-up costs

Suited only to geographic locations with relatively thing ‘crust’ or high volcanic activity

Hydroelectricity



Needs large reservoirs, which may displace people or wildlife

Can be built only in hilly areas with plenty of rainfall


Biomass

The carbon dioxide it releases when it burns has only recently been taken out of the atmosphere by crops

Growing biomass crops instead of food can cause food shortages.

Wood

With careful management, the supply of wood fuel can be maintained indefinitely.

Produces pollution and greenhouse gases.

Wood is more valuable in other sectors rather than producing energy, such as furnitures and buildings.

Non-Renewable Resources:

Advantages Disadvantages

Fossil Fuels

Readily available

Easy to produce

Burning fossil fuels produce greenhouse gases which lead to global warming.

Sulphur causes acid rain.

Nuclear fuel Reliable, clean and

efficient.

Cost of electricity is low.

Expensive to build.

Dangerous.


Section 5: Solids, liquids and gases

a) Units

5.1 use the following units: degrees Celsius (oC), Kelvin (K), joule (J), kilogram/metre3

(kg/m3), kilogram/metre3 (kg/m3), metre (m), metre2 (m2 ), metre3 (m3), metre/second

(m/s), metre/second2 (m/s2 ), newton (N), Pascal (Pa).

Unit of temperature: degrees Celsius (oC)

Unit of temperature: Kelvin (K)

Unit of mass: kilogram/metre3 (kg/m3)

Unit of density: kilogram/metre3 (kg/m3)

Unit of distance: metre (m)

Unit of Area: metre2 (m2)

Unit of Volume: metre3 (m3)

Unit of Speed: metre/second (m/s)

Unit of Acceleration: metre/second2 (m/s2)

Unit of force: newton (N)

Unit of Pressure: Pascal (Pa)

b) Density and pressure

5.2 know and use the relationship between density, mass and volume:

Density is the mass per unit volume of an object or fluid.

5.3 describe experiments to determine density using direct measurements of mass and

volume

Experiment: To determine the density of a regularly-shaped object.

Apparatus: Vernier calipers, ruler, balance

Procedure:


1. Find the mass, using the balance.

2. Determine the volume by taking appropriate measurements and then calculating the volume as

follows:

(a) cuboid – measure the length, breadth and height by using a metre rule or a pair of vernier calipers

V = l x b x h

(b) cylinder – measure the diameter and the length.

V =

(c) sphere – measure the diameter with a pair of vernier calipers or a pair of engineer calipers together

with a metre rule.

(

)

Calculation: If the mass is in g and the volume is in cm3 then,

Precaution: The precaution which need to be taken when using the vernier calipers and the metre rule

apply here.

Experiment: To determine the density of a liquid.

Apparatus: Burrete, beaker, balance, retort stand.

Procedure

1. Find the mass of a clean, dry beaker.

2. Run a volume of the liquid from the burette into the beaker.

3. Find the mass of the beaker and the liquid (m2)

Calculation: If the masses are measured in g, and the volume in cm3, then the density of the liquid

Precaution:

1. When reading the volume of the liquid, make sure that the eye is level with the base of meniscus of

the liquid.

2. Keep the beaker on a plain surface.

Experiment: To determine the density of an irregular shaped object


1. Determine the mass of the object by using a top pan balance.

Now find, find the volume:

2. Pour some water in a measuring cylinder.

3. Mark the position of the lower meniscus of the water level.

4. Put the object into the water. The water level rises.

5. Mark the position of the lower meniscus again

6. Subtract the two readings and get the volume of the object.

Density:

7. Use the equation

to find the density.

5.4 know and use the relationship between pressure, force and area:

The

5.5 understand that the pressure at a point in a gas or liquid which is at rest acts equally in all

directions

Pressure in liquids and gases act equally in all directions, as long as the liquid or gas are not moving.

Experiment: To prove the above statement.

4 holes are made at the same depth in a can. So when it is filled with water, the water flowing from

these holes moves at same speed. This proves that the pressure is equal in all direction.

5.6 know and use the relationship for pressure difference:

pressure difference = height × density × g

p h g


Experiment: To investigate that pressure decreases with height.

Three holes are made at different height of the can. The water from the hole at the bottom-most of the

can travels at highest speed. And the water from top-most hole travels at lowest speed. Thus, proving

that pressure increases with depth.

c) Change of state

5.7 understand the changes that occur when a solid melts to form a liquid, and when a

liquid evaporates or boils to form a gas

What is melting:

Changing state from solid to liquid is called melting.

What is melting point?

At a certain pressure the temperature at which a solid start melting is called melting point. The melting

point of ice is 0oC.

Describe the process of melting.

When a solid is given heat, the vibration of molecules increases. The repulsion between the molecules

increases. Due to greater repulsion than attraction, the molecule take greater equilibrium distance

between them. If we increases temperature more, the equilibrium distance increases more. A situation

comes when the molecules get separated from each other and move randomly, this state is liquid state.

What is boiling?

Changing state from liquid to gaseous state at a certain temperature is called boiling.

What is evaporation?

Changing state from liquid to gas is called evaporation.

What is boiling point?

The temperature at which a liquid start changing to gas is called boiling point.


Describe the process of boiling.

In liquid state the molecule move randomly around the vessel. If we give further heat, the speed of the

molecules increases. If we continue giving heat, a speed reaches when the molecules take off from the

liquid state and change into gaseous state. This is how all liquid changes into gas.

5.8 describe the arrangement and motion of particles in solids, liquids and gases

Features Solid Liquid Gas

Arrangement Regular Irregular Random

Movement Cannot move, vibrate only

Particles can move throughout the liquid slight past each other

Particles can move freely

Energy of Particles Particles have least kinetic energy

Particles have more kinetic energy than solid

The particles have the most kinetic energy

Attraction between particles

Strong Strong Very Weak

Distance between particles (Density)

Tightly packed Tend to stay close together

Far apart

Shape 3D structure Takes the shape of the container

No fixed shape

Compression Cannot be compressed easily.

Cannot be compressed easily.

Can be easily compressed.

d) Ideal gas molecules

5.9 understand the significance of Brownian motion, as supporting evidence for particle

theory

One piece of evidence for the continual motion of particles in a liquid or a gas is called Brownian motion.

Particles of a liquid or gas are moving around continually and bump into each other and into tiny


particles such as pollen grains. Sometimes there will be more collisions on one side of a pollen grain

than on another, and this will make the pollen grain change its direction or speed of movement.

In short:

1. Gases are made up of molecules: We can treat molecules as point masses that are perfect spheres.

Molecules in a gas are very far apart, so that the space between each individual molecule is many orders

of magnitude greater than the diameter of the molecule.

2. Molecules are in constant random motion: There is no general pattern governing either the

magnitude or direction of the velocity of the molecules in a gas. At any given time, molecules are

moving in many different directions at many different speeds.

3. The movement of molecules is governed by Newton’s Laws: In accordance with Newton’s First Law,

each molecule moves in a straight line at a steady velocity, not interacting with any of the other

molecules except in a collision. In a collision, molecules exert equal and opposite forces on one another.

4. Molecular collisions are perfectly elastic: Molecules do not lose any kinetic energy when they collide

with one another.

5.10 understand that molecules in a gas have a random motion and that they exert a force

and hence a pressure on the walls of the container

Pressure comes into play whenever force is exerted on a certain area, but it plays a particularly

important role with regard to gases. The kinetic theory tells us that gas molecules obey Newton’s Laws:

they travel with a constant velocity until they collide, exerting a force on the object with which they

collide. If we imagine gas molecules in a closed container, the molecules will collide with the walls of the

container with some frequency, each time exerting a small force on the walls of the container. The more

frequently these molecules collide with the walls of the container, the greater the net force and hence

the greater the pressure they exert on the walls of the container.

Balloons provide an example of how pressure works. By forcing more and more air into an enclosed

space, a great deal of pressure builds up inside the balloon. In the meantime, the rubber walls of the

balloon stretch out more and more, becoming increasingly weak. The balloon will pop when the force of

pressure exerted on the rubber walls is greater than the walls can withstand.

5.11 understand why there is an absolute zero of temperature which is –273oC

Temperature affect the pressure of particles of gases. The higher the temperature, the higher the

energy in particles and more the pressure. If we decrease the temperature the result will be the exact

opposite. As we cool the gas, the pressure keeps decreasing. The pressure of the gas cannot become

less than zero. The temperature at which the pressure of the gas is decreased to 0, that temperature is

called absolute zero. It is approximately –273oC.

5.12 describe the Kelvin scale of temperature and be able to convert between the Kelvin and

Celsius scales

Temperature in K = temperature in oC + 273


Temperature in oC = temperature in K – 273

5.13 understand that an increase in temperature results in an increase in the average speed

of gas molecules

The kinetic theory explains why temperature should be a measure of the average kinetic energy of

molecules. According to the kinetic theory, any given molecule has a certain mass; a certain velocity;

and a kinetic energy of ½ mv2. As we said, molecules in any system move at a wide variety of different

velocities, but the average of these velocities reflects the total amount of energy in that system. If we

increase the temperature, the kinetic energy will increase. This will result in increase of average velocity

of the gas molecules.

5.14 understand that the Kelvin temperature of the gas is proportional to the average kinetic

energy of its molecules

Temperature in Kelvin is directly proportional to the average kinetic energy of molecules. If we increase

the temperature, kinetic energy as well as pressure will increase as well.

5.15 describe the qualitative relationship between pressure and Kelvin temperature for a

gas in a sealed container

The number of gas particles and the space, or volume, they occupy remain constant. When we heat the

gas the particles continue to move randomly, but with a higher average speed. This means that their

collisions with the walls of the container are harder and happen more often. This results in the average

pressure exerted by the particles increasing.

When we cool a gas the kinetic energy of its particles decreases. The lower the temperature of a gas the

less kinetic energy its particles have – they move more slowly. At absolute zero the particles have no

thermal or movement energy, so they cannot exert pressure.


5.16 use the relationship between the pressure and Kelvin temperature of a fixed mass of

gas at constant volume:

5.17 use the relationship between the pressure and volume of a fixed mass of gas at constant

temperature:

p1V1 = p2V2

Provided the temperature is constant, the average speed of the particles stays the same. If the same

number of particles is squeezed into a smaller volume, they will hit the container walls more often. Each

particle exerts a tiny force on the wall with which it collides. More collisions per second means a greater

average force on the wall and, therefore, a greater pressure.


Section 6: Magnetism and electromagnetism

a) Units

6.1 use the following units: ampere (A), volt (V), watt (W).

Unit of current: ampere (A)

Unit of potential difference: volt (V)

Unit of power: watt (W)

b) Magnetism

6.2 understand that magnets repel and attract other magnets and attract magnetic

substances

Magnets are able to attract objects made from magnetic materials such as iron, steel, etc. Other objects

like plastic, rubber are non-magnetic substance. They can’t attract magnet.

Magnets have two poles: North Pole and South Pole. North Pole and South Pole attract each other.

Similar poles like North Pole and North Pole or South Pole and South Pole repel each other.

6.3 describe the properties of magnetically hard and soft materials

Magnetically hard materials Magnetically soft materials

Needs time to become magnetized Easily gets magnetized

Once magnetized, the magnetism remains permanently

Loses its magnetism easily

Magnets with magnetically hard materials are known as permanent magnets

Magnets with magnetically soft materials are known as temporary magnets

Eg: Steel Eg: Iron

6.4 understand the term ‘magnetic field line’

Magnetic field is a volume of space where magnetism can be detected.

Magnetic fields are drawn using lines of force or flux lines. This lines are imaginary but they:

show the shape of magnetic field.

show the direction of the magnetic field – the field lines travel from north to south.

show the strength of the magnetic field – the field lines are closest together where the magntic

field is strongest.


6.5 understand that magnetism is induced in some materials when they are placed in a

magnetic field

If you keep a material in a magnetic field, eventually after a period of time, that material will be

magnetized.

Example:

Place a magnetically soft material close to a strong magnet. The soft iron bar becomes an

induced magnet with the end nearer the magnet having opposite polarity to that of the magnet.

A steel bar is placed inside a coil. After a while the bar becomes magnetized due to the magnetic

induction from solenoid. The polarities of the magnet depend on the direction of current flow.

6.6 describe experiments to investigate the magnetic field pattern for a permanent bar

magnet and that between two bar magnets

Experiment: To investigate the magnetic field pattern for a permanent bar magnet.

Apparatus: Bar magnet, plotting compass and a plain paper.

Procedure:

1. Place the bar magnet at the centre of the piece of paper so that its N-pole faces North and its S-pole

faces South.

2. Starting near one pole of the magnet, the position ends, N and S, of the compass needle are marked

by pencil dots X and Y. The compass is then moved until one end is exactly over Y and the new position

of other end is marked with a third dot.

3. Repeat the process of marking the dots. Join the series of dots and this will give the plot of the field

lines of the magnetic field.

Precautions:


1. Check that the plotting compass in good working order.

2. Ensure that there is no strong magnetic field around the plotting compass.

Experiment: To plot magnetic field using iron fillings

Apparatus: Iron fillings, Bar magnet

Procedure:

Place a sheet of paper over a bar magnet. Sprinkle a thin layer of Iron filings over the paper and then tap

the paper gently. The iron filings act like thousands of tiny compasses and point themselves along the

lines of flux.

6.7 describe how to use two permanent magnets to produce a uniform magnetic field

pattern.

Apparatus: Two bar magnets

Procedure:

By keeping the opposite poles face each other. The region between the poles would establish magnetic

field that would be uniform.


c) Electromagnetism

6.8 understand that an electric current in a conductor produces a magnetic field round it

When a current flows through a wire a magnetic field is created around the wire. This phenomenon is

called electromagnetism. The field around the wire is quite weak and circular in shape. The direction of

the magnetic field depends up the direction of the current and can be found using the right-hand grip

rule.

6.9 describe the construction of electromagnets

If a temporary magnet is wrapped with a wire into a coil and pass current to it, the magnet will become

magnetized. This way electromagnets can be constructed.

6.10 sketch and recognize magnetic field patterns for a straight wire, a flat circular coil and

a solenoid when each is carrying a current

A field around a straight wire is simply a series of circles around the wire.

A field around a solenoid is similar to that of a bar magnet.

A field around a flat coil is basically like a single wire, but there are two.


6.11 understand that there is a force on a charged particle when it moves in a magnetic field

as long as its motion is not parallel to the field

A charged particle has a magnetic field around it. When a charged particle moves through another

magnetic field, it experiences a force. This is because of the overlapping of the two magnetic fields.

However, if the charged particle is moved parallel to that field, no force will be exerted. As an electric

current is a flow of electrons, we can see this effect when a wire carrying the current is put into a

magnetic field too.

6.12 understand that a force is exerted on a current-carrying wire in a magnetic field, and

how this effect is applied in simple d.c. electric motors and loudspeakers

If we pass a current through a piece of wire held at right angle to the magnetic field of a magnetic field

of a magnet, the wire will move. The motion is the result of forces created by overlapping magnetic field

around the wire and the magnet.

When a current flows along a wire a cylindrical magnetic field is created around the wire. If the wire is

placed between the poles of a magnet, the two fields overlap. In certain places, the fields are in the

same direction and so reinforce each other, producing a strong magnetic field. In other places, the fields

are in opposite directions, producing a weaker field. The wire experiences a force, pushing it from the

stronger part of the field to the weaker part. This is called the motor effect.


The moving – coil loudspeaker:

Signals from a source, such as an amplifier, are fed into the coil of the speaker as currents that are

continually changing in size and direction. The overlapping fields of the coil and the magnet therefore

create rapidly varying forces on the wires of the coil, which cause the speaker cone to vibrate. These

vibrations create the sound waves we hear.


The electric motor:

As current passes around the loop of wire, one side of it will experience a force pushing it upwards. The

other side will feel a force pushing it downwards, so the loop will rotate. Because of the split ring, when

the loop is vertical, the connections to the supply through brushes swap over, so that the current

flowing through each side of the loop changes direction. The wire at the bottom is now pushed upwards

and the wire at the top is pushed downwards – so the loop carries on turning. The arrangement of

brushes and split ring changes the direction of the current flowing through the loop every half turn,

which means the rotation can be continuous.

6.13 use the left hand rule to predict the direction of the resulting force when a wire carries

a current perpendicular to a magnetic field

The left hand rules shows the direction of force, magnetic field and current when a wire carries a current

perpendicularly to a magnetic field.


The pointing finger points the magnetic field from North to South

The middle finger points the direction of current in wire.

The thumb shows the resulting force.

6.14 describe how the force on a current-carrying conductor in a magnetic field increases

with the strength of the field and with the current.

Ways to increase the force produced in motors:

Increase the number of turns or loops of wire (to make a coil)

Increase the strength of magnetic field

Increase the current flowing through the loop of wire

d) Electromagnetic induction

6.15 understand that a voltage is induced in a conductor or a coil when it moves through a

magnetic field or when a magnetic field changes through it and describe the factors which

affect the size of the induced voltage

When a wire cuts the magnetic field of a magnet, a voltage is induced in the wire. This phenomenon is

called electromagnetic induction.

If we move a wire across a magnetic field at right angles, a voltage is induced in the wire. The size of the

induced voltage can be increased by:

1. moving the wire more quickly

2. using a stronger magnet

3. wrapping the wire into a coil so that more pieces of wire move through the magnetic field.

We can generate a voltage and current by pushing a magnet into a coil. The size of induced voltage can

be increased by:


1. moving the magnet more quickly

2. using a stronger magnet

3. using a coil with a larger cross-sectional area.

Faraday’s Law of Electromagnetic Induction:

“The size of the induced voltage across the ends of a wire (coil) is directly proportional to the rate at

which the magnetic lines of flux are being cut.”

This says that:

a voltage and current are generated when a conductor such as wire cuts through the magnetic

field lines.

the faster the lines are cut the larger the induced voltage and current.

6.16 describe the generation of electricity by the rotation of a magnet within a coil of wire

and of a coil of wire within a magnetic field and describe the factors which affect the size of

the induced voltage

In a generator, when the coil rotates, its wire cut through magnetic field lines and a current is induced in

them. If we watch just one side of the coil, we see that the wire moves up through the field and then

down for each turn of the coil. As a result, the current induced in the coil flows first in one direction and

then in the opposite direction. This kind of current is called alternating current. A generator that

produces alternating current is called an alternator. The size of the induced voltage can be increased by

using much stronger magnets, many more turns of wire on the coil and spinning the coil much faster.


6.17 describe the structure of a transformer, and understand that a transformer changes the

size of an alternating voltage by having different numbers of turns on the input and output

sides

A transformer is a device that helps to reduce or increase voltage in a wire or electric line. This is made

of two soft iron core linking to the coils at the two end of the transformer. The first coil is called the

primary coil and the second one is called the secondary coil. When alternating current is passed through

a coil, the magnetic field around it is continuously changing. The changing magnetic field will cut the

secondary coil and induce voltage in it, and that’s how current is passed. If the secondary coil has more

turns than the primary coil, it is a step-up transformer where output the voltage will increase. If the

secondary coil has less turns than the primary, it is a step-down transformer where the output voltage

will decrease.

Why transformer doesn’t work with direct current?


Transformers only work if the magnetic field around the primary coil is changing. Transformers will

therefore only work with ac currents and voltages. They will not work with dc current and voltages.

6.18 explain the use of step-up and step-down transformers in the large- scale generation

and transmission of electrical energy

After generating electricity, electric currents are passed to a step-up transformer which increase the

voltage and decrease the current. This is because higher currents need wide and expensive wire to pass

through. Or else, energy is lost in form of heat. Using transformers mean we can have a solution to this

problem. Before the electricity reaches home, those are passed through step-down transformers to

decrease the voltage and increase the current at the same time.

6.19 know and use the relationship between input (primary) and output (secondary)

voltages and the turns ratio for a transformer:

6.20 know and use the relationship: for 100% efficiency

If a transformer is 100% efficient, the electrical energy entering the primary coil is equal to the electrical

energy leaving the secondary coil.

Input power = output power

VP IP = VS IS


Section 7: Radioactivity and particles

a) Units

7.1 use the following units: Becquerel (Bq), centimetre (cm), hour (h), minute (min), second

(s).

Unit of radioactivity: Becquerel (Bq)

Unit of length: centimetre (cm)

Unit of time: hour (h)

Unit of time: minute (min)

Unit of time: second (s)

b) Radioactivity

7.2 describe the structure of an atom in terms of protons, neutrons and electrons and use

symbols such as 146C to describe particular nuclei

An atom is a tiny particle with nucleus in the centre and electrons orbiting it. A nucleus is made up of

proton and neutron.

An atom is presented in this way = XYZ

Z=Symbol of the atom

X=Mass Number

Y=Atomic Number


7.3 understand the terms atomic (proton) number, mass (nucleon) number and isotope

Atomic Number: Atomic number is the number of protons in an atom

Mass number: Mass number is the addition number of protons and neutrons

Isotope: Isotope is an element which has the same atomic number as the original atom but different

mass number.

7.4 understand that alpha and beta particles and gamma rays are ionising radiations emitted

from unstable nuclei in a random process

Stability of isotopes: The protons are held in a nucleus by nuclear force. Nuclear force is strong short

ranged force. On the other hand, the protons try to repel away from each other due the electric force

formed by the similar charges of protons. So the presence of neutrons help nucleus to stabilize. Too

many or too few of neutrons can cause instability and may eventually decay, thus giving out ionising

radiation along with energy.

Ionising radiation: When unstable nuclei decay they gives out ionising radiation. Ionising radiation

causes atom to gain or lose electrons to form ions. Basically there are three types of ionizing radiation:

alpha, beta and gamma.

Alpha radiation: Alpha radiation consists of fast-moving helium nucleus.

Beta radiation: Beta radiation consists of fast-moving electron.

Gamma rays: Gamma ray is an electromagnetic wave.

7.5 describe the nature of alpha and beta particles and gamma rays and recall that they may

be distinguished in terms of penetrating power

Nature of radiation

Alpha radiation has been identified as a stream of helium nuclei. In other words, an alpha particle is

actually a positively-charged helium nucleus comprising two protons and two neutrons. It is a very

stable particle.

Beta radiation has been identified as a stream of high-energy electrons. In other words, a beta particle is

actually a negatively-charged electron. It is formed by a nucleus decay process.

Gamma radiation has been identified as high-frequency electromagnetic radiation. In other words, they

are electromagnetic waves of very short wavelength.

Ionising power

When a fast-moving particle such as an alpha or beta particle collides with an atom, an electron may be

ejected from the atom, resulting in a charged ion. Alpha particles have the greatest ionising power

compared to beta and gamma radiation because it is heavier and large and is more likely to collide with


atoms, resulting the greatest number of ions in their tracks. Compared with gamma rays, beta particles

are more ionizing.

Penetrating power

The Figure shows the relative penetrating power of three kinds of radiation. The alpha particles can be

stopped by a sheet of paper whereas beta particles and gamma rays penetrate it easily. This shows that

alpha particles have the least penetrating power. Infact, it has a range of only few centimeters in air.

Beta particles have a range of several metres in air but can be stopped by a 5mm tick aluminium sheet.

Gamma rays are the most penetrating, having a range of a few hundred metres in air and can only be

stopped by a 2 cm-thick lead shield.

Radiation Ionising power Penetrating range in air

Example of range in air

Radiation stopped by

Alpha,α strong weak 5-8cm paper

Beta, β medium medium 500-1000 cm Thin aluminium

Gamma, γ weak strong Virtually infinite Thick lead sheet

7.6 describe the effects on the atomic and mass numbers of a nucleus of the emission of each

of the three main types of radiation

Alpha (α) decay:

In alpha decay, alpha particles takes away 4 nucleons with itself which reduce the mass number of the

element by 4. Alpha particles have 2 protons with it, which reduce the atomic number of the element by

2.

Example:


Beta (β)decay:

Beta particle is formed when a neutron splits to form a proton and an electron. Beta particle practically

has no mass, so it doesn’t affect the mass number of the element. As beta particles have a charge of -1,

the elements atomic number is increased by +1.

Example:

Gamma (γ) decay:

After an unstable nucleus has emitted an alpha or beta particle it sometimes has surplus energy. It emits

this energy as gamma radiation. Gamma ray is an electromagnetic wave and doesn’t affect the mass

number or atomic number of the element.

7.7 understand how to complete balanced nuclear equations

In a nuclear equation, in the left hand side the total mass number should be equal to the mass number

in the right hand side. And the atomic number should be equal in both sides.

Here, Uranium experienced an alpha decay:

Here, Lithium faced beta decay:


7.8 understand that ionising radiations can be detected using a photographic film or a

Geiger-Muller detector

Photographic film: Photographic film is a traditional way to detect presence of ionising radiation nearby.

Ionising radiations imprints photographic plates. That is the film becomes foggy when it is exposed to a

certain amount of radiation.

Geiger Muller: Geiger Muller tube is used to measure the level of radiation. It is a glass tube with an

electrically conducting coating on the inside surface. The tube has a thin window made of mica. The

tube contains low pressured gases. In the middle of the tube, there is an electrode which is connected

to a high voltage supply via a resistor. When ionising radiation enters the tube through the glass, it

causes the low pressured gas to form ions. As ions are charged particle they allow to flow a pulse of

current in the electrode which is detected by an electronic circuit.

Counting circuit is fitted with a GM tube so that it can measure how many ionising particles entered GM

tube. Rate meters are fitted with GM tube to measure the number of ionising events per second, and so

give a measure of the radioactivity in Becquerels. Rate meters have a loudspeaker output so the level of

radioactivity is indicated by the rate of clicks produced.

7.9 explain the sources of background radiation

Background radiation is low-level ionizing radiation that is produced all the time. The background

radiation has many sources including natural and artificial ones.

Natural sources:

Cosmic rays: Violent nuclear reactions in stars and exploding stars called supernovae produce very

energetic particles and cosmic rays that continuously bombard the Earth. Lower energy cosmic rays are

given out by the Sun. Our atmosphere gives us fairly good protection from cosmic rays.

Rocks and soil: Some of the radiation comes from rocks in the Earth’s crust. When the Earth was

formed, around 4.5 billion years ago, it contained many radioactive isotopes. Some decayed very quickly

but others are still producing radiation. Some of the decay products of these long-lived radioactive


materials are also radioactive, so there are radioactive isotopes with much shorter half-lives still present

in the Earth’s crust.

Living things: Plants absorb radioactive materials from the soil and these pass up the food chain. Also

we breathe small amount of radioactive isotopes of carbon, carbon – 14. We continuously renew the

amount of radioactive isotopes in our bodies.

Artificial sources:

Human activity has added to background radiation by creating and using artificial sources of radiation.

These include radioactive waste from nuclear power stations, radioactive fallout from nuclear weapons

testing and medical x-rays.

Artificial sources account for about 15 percent of the average background radiation dose. Nearly all

artificial background radiation comes from medical procedures such as receiving x-rays for x-ray

photographs.

7.10 understand that the activity of a radioactive source decreases over a period of time and

is measured in Becquerels

Radioactive substance keeps decaying in a random process. As it decays, its activity is reduced over a

period of time. The unit of Radioactivity is Becquerels.


If we plot a graph of activity of a radioactive isotope against time we will get something like the one

above. The graph falls steeply at first and more slowly after time. This is because the activity gets

smaller, and the smaller the activity the slower the activity will decrease. This kind of decrease

proportional of activity to time is called exponential decay.

7.11 understand the term ‘half-life’ and understand that it is different for different

radioactive isotopes

“Half-Life” is the amount of time taken for the activity of any radioactive substance to reduce to half.

Each radioactive isotope decays in different speeds. So half life is different for different types of

isotopes.

7.12 use the concept of half-life to carry out simple calculations on activity


To find half life, plot graph of the activity against time. Point out the half of the activity and draw line to

match the time as done in the figure. The time is your half-life.

Half life calculation:

Example: The half life of an isotope is 3 hours. If the initial activity of the isotope is 544 Bq, what will be

the count rate after 15 hours?

Ans:

15 hours = 3 x 5 hours

Therefore, the activity will be halved 5 times.

17

The activity will be 17 Bq after 15 hours.

Experiment: How to find the Half-life of a radioactive isotope.

Apparatus: Geiger-Muller tube

Procedure: To measure the half-life of a radioactive material we must measure the activity of the

sample at regular times. This is done using a Geiger – Muller tube linked to a rate meter. Before taking

measurements from the sample, we must measure the local background radiation. We must subtract

the background radiation from measurements taken from the sample so we know the radiation

produced by the sample itself. We then measure the rate of decay of the sample at regular time

intervals. The rate of decay is shown by the count rate on the rate meter. The results should be recorded

in a table.

The rate of decay corrected from background radiation is proportional to the amount of radioactive

isotope present. If we plot a graph of rate of decay against time, we can measure the half-life from the

graph.


7.13 describe the uses of radioactivity in medical and non-medical tracers, in radiotherapy,

and in the radioactive dating of archaeological specimens and rocks

Radioactive materials are being used in many different ways in medicine, industry and agriculture. There

are five main uses of radioactive materials. They are used in tracers, as penetrating radiation, as power

sources, for medical treatment and for dating archaeological specimens.

1. Tracers

The ability of detectors to measure small concentrations of a radioactive material is made use of

in tracer applications. Tracers are used extensively in medicine. Iodine, for example accumulates

readily in the thyroid gland. By using radioactive iodine – 131 and finding out the rate at which it

accumulates in the thyroid, the thyroid functions may be monitored.

In industry, a typical use of tracers is in the study of the wear and tear of the moving parts of

machinery. This can be done by tagging a radioisotope onto the surfaces of the moving parts

under investigation and then finding the amount rubbed off. Another major use in industry is in

the detection of leaks in underground pipe.

By introducing a suitable radioactive tracer into the pipe, the leak unusually high count rate at

the area of the leak. This will save both time and money in locating and repairing the leak.

In agriculture, radioactive phosphorus-32 is used as a tracer to find out how well the plants are

absorbing phosphates which are crucial to their growth. The complicated mechanism of

photosynthesis has also been studied using tracers.

2. Penetrating radiation

Cobal-60 emits penetrating gamma rays which can be used to penetrate deep into welding to

reveal faults. Normal X-rays are not able to perform this task. Gamma rays are also used to

photograph the inside of an engine to reveal any cracks.

In the area of manufacturing, suitable radioactive sources are used to check the thickness of

rolled sheets of metal, paper or plastic. In other words, the gamma radiation source acts as a

thickness gauge.

A beta source cannot be used in this case because it is not penetrative enough when compared

to the gamma source. However, a beta source can be used to check the thickness of rolled

sheets of paper or plastic.

In the food industry, the high penetration power of gamma rays is used to kill any bacteria in

pre-packaged or frozen foods. This will sterilize the food and prevent food poisoning.

3. Power sources

Uranium-235 is the most common fuel in nuclear power stations. Other radioactive materials


can be used as portable sources. For example, some satellites use radioactive materials as their

source of power, which comes from the energy released when these radioactive materials

decay.

Some fire alarms contain a small amount of alpha-emitting substance. The alpha particles

emitted keep the air in the fire alarms slightly ionized and any changes in the level of ionization

caused by smoke in a fire can be detected and the alarm is set off.

4. Medical treatment

Radioactive cobalt, Co-60, decays with the emission of beta particles and high energy gamma

rays. When properly shielded, the gamma rays can be brought to bear on deep cancerous

growths in a cancer patient. The radiation kills the cell of the malignant tumour in the patient

Machines built for this purposes, known as gammatrons are very useful in radiotherapy.

5. Archaeological dating

Radioactive carbon-14 is present in small amounts in the atmosphere. Living plants absorb

carbon dioxide and therefore become slightly radioactive. This enables the level of radioactivity

of plants to be monitored.

When a tree dies, the radioactive carbon present inside it will begin to decay. Since the half-life

of carbon-14 is nearly 5500 years the age of a dead tree can be found by comparing the activity

of the carbon-14 in the dead tree and a living tree.

The activity of the carbon-14 of a living tree stays fairly constant as the carbon-14 is being

replenished while the carbon-14 in the dead tree is not replenished. Therefore, by measuring

the activity of carbon-14 in an ancient relic, scientists can calculate its age.

7.14 describe the dangers of ionising radiations, including:

Radiation can cause mutations in living organisms

Radiation can damage cells and tissue

The problems arising in the disposal of radioactive waste

and describe how the associated risks can be reduced.

Hazard of radiation

Overexposure to radioactive radiation may result in radiation burns. These will lead to sores and blisters

which may take a long time to heal. Extreme overexposure can lead to radiation sickness, and ultimately

death. Radioactive radiation can also lead to delayed conditions such as eye cataracts or leukemia,

which may only appear many years later.

Ionizing radiation causes mutations in the genes which led to offspring bearing physiological and other

abnormalities. They are health hazards to people, livestock and plants.


Precautions against radiation hazards

To prevent overexposure to radiation or any accidents, following precautions need to be taken:

i) Workers working with gamma radiation must wear film badges or pocket dosimeter in order to

keep tract of the accumulated dosage they are exposed to over given period time.

ii) Always keep radioactive sources in lead-lined boxes. The wall of the storage rooms of nuclear

laboratories are to be built with lead bricks that are 1m thick. The outside of the room must be

labeled “Radioactive Material”

iii) The radiation symbol must be displayed whenever an experiment with a radioactive source is

conducted.

iv) If possible, persons doing radiation experiments should use special, protective clothing such as

lead-lined suits as well as wear lead-lined gloves. Tweezers must be used to pick up strong

sources. After completion of the day’s work, the contaminated clothing must be changed.

v) Food and drinks are strictly prohibited when a person is doing a radioactivity experiment.

Otherwise, radioactive dust can be taken into the body together with food.

vi) The nuclear process in a reactor produces a variety of different types of radioactive material.

Some have relatively short half-lives and decay rapidly. These soon become safe to handle and

do not present problems of long-term storage. Other materials have extremely long half – lives.

These will continue to produce dangerous levels of ionising radiation for thousands of years.

These waste products present a serious problem for long-term storage. They are usually sealed

in containers that are then buried deep underground. The sites of underground storage have to

be carefully selected. The rock must be impermeable to water and the geology of the site must

be stable – storing waste in earthquake zones or area of volcanic activity would not be sensible.

c) Particles

7.15 describe the results of Geiger and Marsden’s experiments with gold foil and alpha

particles

Geiger and Marsden made an experiment with alpha particle. They shoot alpha radiation to a thin gold

foil. The gold foil was surrounded by zinc sulphide screen which detected the presence of alpha

particles. The result was, most of the alpha particles went straight through the foil, some bended a little

bit and very few deflected at high angles.


7.16 describe Rutherford’s nuclear model of the atom and how it accounts for the results of

Geiger and Marsden’s experiment and understand the factors (charge and speed) which

affect the deflection of alpha particles by a nucleus

After the experiment of Geiger and Marsden, Rutherford came to a conclusion that most of alpha source

went through the foil was through empty space of atoms. Other deflection occurred because of the

nucleus which is positively charged and so is alpha particle. That’s why they repelled each other and

deflected. Rutherford gave the evidence that an atom is consisted of a positive nucleus in the centre and

rotating electron outside in the mostly empty space.

7.17 understand that a nucleus of U-235 can be split (the process of fission) by collision with

a neutron, and that this process releases energy in the form of kinetic energy of the fission

products

Fission: If unstable nuclei split up to form stable nuclei, the process is called Fission. Urnaium-235 can

also be split up by collide a neutron with the nuclei. As it is done so, the nucleus becomes unstable and

split up to form Krypton and Barium (stable atoms) and three nucleus and gamma rays.

7.18 understand that the fission of U-235 produces two daughter nuclei and a small number

of neutrons

When a radioactive isotope splits it forms one or more stable nuclei which are called daughter nuclei.

Uranium-235 produces two daughter nuclei of barium-144 and krypton-89 and three neutron.

7.19 understand that a chain reaction can be set up if the neutrons produced by one fission

strike other U-235 nuclei

When a U-325 splits, it gives out three neutrons. This three neutrons again hit other uranium nucleus

and gives out nine neutrons. These nine neutrons hits other nuclei and keep on continuing fission

reacted. This type of reaction is called chain reaction.

7.20 understand the role played by the control rods and moderator when the fission process

is used as an energy source to generate electricity.


Fuel rod: The reactor core contains fuel rod of enriched uranium. Enriched uranium is uranium – 238

with a higher proportion of uranium – 235 than is found in natural reserves of uranium.

Moderator: Graphite is used as moderator. The job of the moderator is to absorb some of the kinetic

energy of the neutrons to slow them down. This is because slow neutrons are more easily absorbed by

uranium – 235. A neutron slowed in this way can start the fission process.

Control rods: In the nuclear reactor there are also control rods, made of boron or cadmium. These

absorb the neutrons and take them out of the fission process completely. When control rods are fully

inserted into the core, the chain reaction is almost completely stopped and the rate of production of

heat is low. As the control rods are withdrawn, the rate of fission increases producing heat at a greater

rate.


Appendix 1: Electrical circuit symbols


Appendix 2: Physical units

Units

Speed m/s

Velocity m/s

Acceleration m/s2

Distance M

Time S

Force N

Mass Kg

Weight N

Momentum Kg m/s

Moment Nm

Power W

Current A

Voltage V

Energy J

Charge C

Frequency Hz

Time period S

Wave speed m/s

Wavelength M

Critical angle o

Work done J

Gravitational field strength N

Density Kg/m3

Volume M3

Pressure Pa

Area M2

Height M

Temperature oC

Radioactivity Bq


Appendix 3: Formulae and Relationships

1.

2.

3.

4.

5. Momentum = mass x velocity

6.

7.

8. Moment = Force x distance

9. Sum of clockwise moments = sum of anticlockwise moments

10. Power = Current x Voltage

11. Energy = power x time

12. Voltage = current x resistance

13. Charge = current x time

14.

15.

16.

17. i

18.

19. Work done = force x distance

20. Gravitational potential energy = mass x gravitational field strength x height

21. Kinetic energy = ½ mv2

22.

23.

24.

25.

26. P1 V1 = P2 V2

27. Temperature in K = temperature in oC +273

28.

29. Vp / Vs = np / ns

30. Power input = Power out

31. Voltage in primary current x Current in primary current = Voltage in secondary current x Current

in secondary current

32.

33.


Appendix 1: Glossary (131) Acceleration

The rate of increase of velocity with time.

air resistance (drag)

The force opposing the motion of bodies

moving through air.

alpha particle

A type of nuclear radiation consisting of a

helium nucleus ejected from an unstable

nucleus.

alternating current

A current that continually changes direction.

ammeter

An instrument used to measure the size of

current in a circuit.

amp

The SI unit of electric current.

amplified

Increased in size or power.

analogue electrical signals

Electrical signals, usually voltages, that have

continuously variable values.

angle of incidence

The angle measured between a ray of light

arriving at a surface and the normal.

angle of reflection

The angle measured between a ray of light

reflected at a surface and the normal.

balanced

Equal in size but opposite in sign, therefore

summing to zero (i.e. balanced forces,

balanced charge.)

becquerel

The rate of disintegration of a radioactive

substance; one disintegration per second.

beta particle

A type of nuclear radiation consisting of a

high speed electron emitted from an unstable

nucleus.

braking distance

The distance a vehicle travels before coming

to rest after the brakes have been applied.

Brownian motion

The continuous, random, jerky motion of

pollen grains observed by the botanist

Robert Brown.

cell mutation

A change in the function of a living cell,

sometimes caused by ionizing radiation.

centre of gravity

The point in a body through which the

whole of its weight appears to act.


chain reaction

An escalating nuclear process in which each

decay of an unstable nucleus triggers two or

more unstable triggers two or more unstable

nuclei to decay.

circuit breakers

The modern equivalent of fuses, designed to

break the conducting path in a circuit when a

set current is exceeded. They may be reset

by the push of a switch once the fault

causing them to operate is remedied.

comet

A relatively small ice and rock body orbiting

the sun with a very elongated (eccentric)

orbit. Comets have a distinctive tail.

conductors (electrical)

Materials that allow electricity to pass

through them easily. Most metals are good

electrical conductors.

contact force

The forces acting on bodies in contact.

control rods

Control rods are used in a nuclear reactor to

slow down the rate of nuclear fission or to

stop the fission process completely.

controlled nuclear fission

Involves the slow and useful release of

energy in a nuclear reactor.

critical angle

Light arriving at a boundary between any

material, in which light travels more slowly

than in air, and air at an angle greater than

the critical angle is totally internally

reflected.

current

The rate of flow of electric charge.

density

The mass per unit volume of a substance.

diffraction

The curving of waves as they pass the edges

of objects.

digital electrical signals

A digital signal has only two possible

values. In computer and communication

systems these values are 0 V and 5 V.

displacement

Distance moved in a specific direction; a

vector quantity.

distance

Distance moved without considering

direction; a scalar quantity.

double insulated

Having an outer casing which is an electrical

insulator; having no exposed metal casing.

drag force

The force that opposes the motion of an

object through a gas or liquid.


earthed

Having a very low resistance connection to

the general mass of the earth, taken as

always being a 0 V.

efficiency

A measure of how effectively energy is

transformed into a useful form.

elastic

Able to return to its original size and shape

after being deformed.

elastic limit

This is taken as the point that a stretched

spring or wire no longer obeys Hooke's

Law. This is the limit of proportionality.

electric charge

The property of particles that causes electric

effects.

electromagnetic (EM) waves

Waves that require no material medium in

which to travel. They carry energy as

variations in the magnetic and electric fields

in space.

electromagnetic spectrum

The family of EM waves, ranging from

radio waves to gamma and cosmic rays.

electron

Extremely small particle carrying negative

charge and making up the outer 'shell' or

'shells' of an atom.

endoscope

A fibre optic device used to image the inside

of living bodies as a diagnostic tool.

energy

Energy exists in many forms - heat, light

etc; it is required to do work.

evaporation

The process by which liquids change into

gases.

extension

In springs this is the increase in length that

results from applying a force to stretch the

spring.

fissile

Referring to unstable materials; something

that can readily be split or will split

spontaneously.

force

A push or pull. When a force is applied to a

body it will cause a change in the state of

motion of the body, making it accelerate,

decelerate or change direction. Forces can

also change the shape of an object.

fossil fuels

Fuels formed from dead organic matter over

millions of years; examples are gas, oil, and

coal. These are non-renewable energy

sources.

free electrons

Electrons which are not bound to any

particular atom in a solid. These are free to


move and enable charge to move through a

material forming an electric current.

frequency

The number of waves produced in one

second. More generally, how many times

something occurs per second.

friction

The force that opposes motion between two

surfaces.

fuse

A length of wire designed to melt when a

specified current value is exceeded, thus

breaking the circuit.

galaxy

A group of many billions of stars rotating

around a common centre.

gamma rays

Highly penetrating electromagnetic radiation

produced when an unstable atom

disintegrates.

geothermal energy

Heat energy produced by nuclear processes

in the earth's core.

gradient

The slope of a graph line measured as the

rate of increase of the y-axis variable with

respect to the x-axis variable.

gravitational field strength

The force in newtons exerted per kilogram

of mass by gravity. At the Earth's surface

this is approximately 10N/kg.

half-life

The time taken for half of the atoms in a

sample of radioactive material to decay

(disintegrate).

hard magnetic materials

Materials that retain their magnetism well.

hydroelectric power

Power produced using the potential energy

of water stored in reservoirs in mountainous

regions.

hydroelectricity

Electricity produced by generators using

hydroelectric power.

inelastic

Materials that are unable to return to their

original shape after deformation by a force.

infrared

A part of the EM spectrum. The radiation

emitted by hot objects.

insulators (electrical)

Materials that electricity cannot pass

through.


joule

The SI unit of energy. 1 joule is the amount

of work done (energy transferred) when a

force of 1 newton is applied through a

distance of 1 metre.

Kelvin temperature scale

The scale of temperature with zero set at the

lowest possible temperature that can be

achieved: absolute zero. This is -273° on the

Celsius scale.

light waves

A part of the EM spectrum that can be

detected by the human eye.

longitudinal waves

Waves in which the particles of the medium

move backwards and forwards along the

same line as the direction of transfer of

energy.

loudness

The power or strength of a sound. Loudness

depends on the amplitude of the vibrations

of the sound wave.

magnetic

Possessing the ability to attract iron and its

compounds.

mechanical waves

Waves that require a material medium

through which energy may be transferred.

microwaves

A part of the EM spectrum. Used to directly

heat water in telecommunication systems.

moderator

A material used in nuclear reactors to

produce 'slow' neutrons needed to trigger

nuclear fission. Graphite and heavy water

are typical moderators.

moons

Natural satellites held in orbits around

planets by the force of gravity.

Motor Rule

The rule devised by Fleming to predict the

direction of the force produced on a wire

when it carries current in a magnetic field

(provided the direction of current is

perpendicular to the magnetic field).

negative electric charge

The type of charge possessed by the

electron.

neutral

Having no overall electric charge. Neutrons

are electrically neutral because there is a

balance between the number of negative

charges on electrons and the number of

positive charges on the protons which make

up part of the nucleus.

neutron

Uncharged particle found in the nucleus of

atoms.

normal

Perpendicular to, as in the normal drawn as

a construction line.


normal reaction

A contact force acting at right angles to a

surface.

ohm (Ω)

Unit of resistance; the resistance of a

conductor that passes a current of 1 amp

when a voltage of 1 volt is applied across it.

optical fibre

A thin glass tube designed to carry

information in the form of light through total

internal reflection.

parallel circuit

A circuit with two or more conducting paths

between any two points in the circuit.

parent nuclide

An unstable nucleus that decays and splits

into two or more lighter nuclei. The lighter

nuclei are called daughter nuclides.

partially elastic

Description of a collision in which kinetic

energy is not conserved after the colliding

bodies have separated.

period

The time taken for one complete cycle of an

oscillation or wave.

pitch

How high a musical note is. This is related

to the frequency of the sound - the higher

the frequency the higher the pitch.

planets

Massive objects held in regular orbit around

a star by the force of gravity.

positive electric charge

The type of charge possessed by the proton.

power

The rate of transfer or conversion of energy.

pressure

Force acting per unit area.

proton

A positively charged particle found in the

nucleus of an atom.

radio waves

A part of the EM spectrum. Used in

communication and radio and TV

transmission.

randomly

Unpredictably.

reaction time

The time taken until there is a conscious

response in humans to some event or

stimulus.

resistance

A measure of how difficult it is for current

to pass through a part of a circuit. Measured

in ohms.


resultant force

The net force acting on a body when two or

more forces are unbalanced.

Sankey diagrams

Diagrams to represent the relative size of

energy conversions that take place in a

process or system.

satellites

Man-made objects held in orbit around a

planet by the force of gravity.

scalar

A quantity with magnitude (size) but no

specific direction. Examples: energy, mass.

second

The base unit of time measurement.

series circuit

A circuit with only one path for an electric

current to flow.

soft magnetic materials

Materials that are easy to magnetize and

demagnetize.

solar power

Power obtained from the energy transferred

by the EM waves from the Sun.

sound waves

Longitudinal waves in gases, liquids and

solids with frequencies in the range 20 Hz to

20 kHz.

speed

Distance travelled per unit time.

star

Huge nuclear fission explosions releasing

vast amounts of energy as light, heat, and

other forms of EM radiation.

tension

The force in stretched materials.

thermal radiation

Heat radiation. EM waves with frequencies

in the infrared range, lower than the red end

of the visible spectrum.

thinking distance

The travelled by a moving vehicle in the

time that it takes for the driver to react to an

emergency before applying the brakes.

tidal power and wave energy

Power obtained from the rise and fall of the

oceans due to tidal motion and from the

waves which result from tidal and wind

action on the oceans.

transformers

Electromagnetic devices used to increase or

decrease the size of alternating voltage

electricity supplies.

transverse waves

Waves in which the particles of the medium

move at right angles to the direction of

transfer of energy. Although EM waves do

not require a material medium in which to

travel, these are also transverse waves.


ultraviolet

The part of the EM spectrum with

frequencies greater than the blue end of the

visible spectrum.

unbalanced

Not adding up to zero (i.e. unbalanced

forces have a non-zero resultant or sum)

uncontrolled nuclear fission

Involves the release of vast amounts of

energy in a very short time, in short an

explosion.

universe

The system comprising every galaxy.

upthrust

The upward force that acts on an object

because it has displaced a volume of liquid

or gas.

vector

A quantity that has both size (magnitude)

and direction. Examples: velocity,

acceleration, and force.

velocity

The rate of increase of distance travelled in a

specified direction with time.

virtual image

The image formed in mirrors that appears to

be behind the mirror. Any image that is not

the actual source of real rays of light.

viscous drag

The force that opposes the motion of an

object through a liquid.

visible light

EM waves in the range of frequencies that

can be detected by the human eye.

volt

The unit of voltage. 1 volt is equal to 1 joule

of energy per coulomb of charge passed

through a component.

voltage

A measure of the energy converted per unit

charge passing through a component. also a

measure of the amount of energy transferred

to electrical form per unit by an electrical

power supply, like a battery.

voltmeter

A measuring instrument for measuring the

voltage between two points in a circuit.

watt

The unit of power equal to a rate of transfer

of energy of 1 joule per second.

weight

The force acting on a body due to its

presence in a gravitational field.

wind power

Power obtained from the kinetic energy of

moving air.


work

The transfer of energy to a body.

Mechanical work is the transfer of energy

which occurs when a force is applied

through a distance in the direction of the

force.

X-rays

EM waves in the range of frequencies

beyond the ultraviolet range. EM waves that

can pass through low density materials like

flesh, but which are absorbed by more dense

materials like bone.

shawon notes | · apparatus: toy car or tennis ball, meter rule, slotted masses, stopwatch,...

Documents